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#include <bits/stdc++.h>
namespace IO {
inline char read() {
static const int IN_LEN = 1000000;
static char buf[IN_LEN], *s, *t;
s == t ? t = (s = buf) + fread(buf, 1, IN_LEN, stdin) : 0;
return s == t ? -1 : *s++;
}
template <typename T>
inline void read(T &x) {
static char c;
static bool iosig;
for (c = read(), iosig = false; !isdigit(c); c = read()) {
if (c == -1) return;
c == '-' ? iosig = true : 0;
}
for (x = 0; isdigit(c); c = read()) x = x * 10 + (c ^ '0');
iosig ? x = -x : 0;
}
inline void read(char &c) {
while (c = read(), isspace(c) && c != -1)
;
}
inline int read(char *buf) {
register int s = 0;
register char c;
while (c = read(), isspace(c) && c != -1)
;
if (c == -1) {
*buf = 0;
return -1;
}
do
buf[s++] = c;
while (c = read(), !isspace(c) && c != -1);
buf[s] = 0;
return s;
}
const int OUT_LEN = 1000000;
char obuf[OUT_LEN], *oh = obuf;
inline void print(char c) {
oh == obuf + OUT_LEN ? (fwrite(obuf, 1, OUT_LEN, stdout), oh = obuf) : 0;
*oh++ = c;
}
template <typename T>
inline void print(T x) {
static int buf[30], cnt;
if (x == 0) {
print('0');
} else {
x < 0 ? (print('-'), x = -x) : 0;
for (cnt = 0; x; x /= 10) buf[++cnt] = x % 10 | 48;
while (cnt) print((char)buf[cnt--]);
}
}
inline void print(const char *s) {
for (; *s; s++) print(*s);
}
inline void flush() { fwrite(obuf, 1, oh - obuf, stdout); }
struct InputOutputStream {
template <typename T>
inline InputOutputStream &operator>>(T &x) {
read(x);
return *this;
}
template <typename T>
inline InputOutputStream &operator<<(const T &x) {
print(x);
return *this;
}
~InputOutputStream() { flush(); }
} io;
}
namespace {
using IO::io;
const int MAXN = 10100;
const int MAXM = 20000;
const int INF = INT_MAX >> 1;
struct Node {
int v, f, index;
Node(int v, int f, int index) : v(v), f(f), index(index) {}
};
struct Graph {
typedef std::vector<Node> Vector;
Vector edge[MAXN + 1];
inline void addEdge(const int u, const int v, const int f) {
edge[u].push_back(Node(v, f, edge[v].size()));
edge[v].push_back(Node(u, 0, edge[u].size() - 1));
}
inline void clear(const int n) {
for (register int i = 0; i <= n; i++) edge[i].clear();
}
inline Vector &operator[](const int i) { return edge[i]; }
};
struct ImprovedShortestAugmentPath {
Graph g;
int h[MAXN + 1], gap[MAXN + 1];
inline int sap(int v, int flow, int s, int t, int n) {
if (v == t) return flow;
register int rec = 0;
static int iter[MAXN + 1];
for (register int i = iter[v]; i < g[v].size(); i++) {
Node *p = &g[v][i];
if (p->f > 0 && h[v] == h[p->v] + 1) {
register int ret =
sap(p->v, std::min(p->f, flow - rec), s, t, n);
p->f -= ret, g[p->v][p->index].f += ret, iter[v] = i;
if ((rec += ret) == flow || h[v] >= n) return iter[v] = 0, rec;
}
}
if (!(--gap[h[v]])) h[s] = n;
gap[++h[v]]++, iter[v] = 0;
return rec;
}
inline int sap(int s, int t, int n) {
register int ret = 0;
memset(gap, 0, sizeof(int) * (n + 1));
memset(h, 0, sizeof(int) * (n + 1));
for (gap[0] = n; h[s] < n;) ret += sap(s, INF, s, t, n);
return ret;
}
int n, m, s, t;
int u[MAXM + 1], v[MAXM + 1], c[MAXM + 1], d[MAXM + 1];
int in[MAXN + 1], out[MAXN + 1];
inline bool check(int mid) {
register int sum = 0;
g.clear(n + 1);
memset(in, 0, sizeof(int) * (n + 1));
memset(out, 0, sizeof(int) * (n + 1));
for (register int i = 1; i <= m; i++) {
if (c[i] <= mid) out[u[i]]++, in[v[i]]++;
if (d[i] <= mid) g.addEdge(v[i], u[i], 1);
}
for (register int i = 1; i <= n; i++)
if (std::abs(in[i] - out[i]) & 1) return false;
for (register int i = 1, x; i <= n; i++) {
x = (in[i] - out[i]) / 2;
if (x > 0) g.addEdge(s, i, x), sum += x;
if (x < 0) g.addEdge(i, t, -x);
}
register int tmp = sap(s, t, t + 1);
return tmp == sum;
}
inline void solve() {
io >> n >> m;
register int l = INT_MAX, r = INT_MIN;
s = 0, t = n + 1;
for (register int i = 1; i <= m; i++) {
io >> u[i] >> v[i] >> c[i] >> d[i];
if (c[i] > d[i]) std::swap(c[i], d[i]), std::swap(u[i], v[i]);
l = std::min(l, c[i]), r = std::max(r, d[i]);
}
l--, r++;
while (r - l > 1) {
register int mid = l + r >> 1;
if (check(mid))
r = mid;
else
l = mid;
}
if (!check(r))
io << "NIE";
else
io << r;
}
} task;
}
int main() {
task.solve();
return 0;
}
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