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| #include <cstdio>
#include <cstring>
#include <queue>
using namespace std;
const int N = 125100;
int n, m, s, t, tot = 1, hd[(int)6e4], cur[(int)6e4], ss, tt, dep[(int)6e4];
long long flow[(int)6e4], l[N];
struct Edge
{
int to, nxt;
long long val;
} e[N * 3 + 99];
inline void add(int u, int v, long long w)
{
e[++tot] = {v, hd[u], w}, hd[u] = tot;
e[++tot] = {u, hd[v], 0ll}, hd[v] = tot;
}
bool bfs(int st, int en)
{
for (int i = 0; i <= n + 2; ++i)
dep[i] = 0;
queue<int> q;
memcpy(cur, hd, sizeof(hd));
q.push(st);
dep[st] = 1;
while (!q.empty())
{
int u = q.front();
q.pop();
for (int eg = hd[u]; eg; eg = e[eg].nxt)
{
if (!dep[e[eg].to] && e[eg].val > 0)
{
dep[e[eg].to] = dep[u] + 1;
q.push(e[eg].to);
}
}
}
return !!dep[en];
}
long long dfs(int u, int en, long long flow)
{
if (u == en)
return flow;
long long r = flow;
for (int eg = cur[u]; eg && r; eg = e[eg].nxt)
{
cur[u] = eg;
if (e[eg].val > 0 && dep[e[eg].to] == dep[u] + 1)
{
long long c = dfs(e[eg].to, en, min(r, e[eg].val));
r -= c;
e[eg].val -= c;
e[eg ^ 1].val += c;
}
}
return flow - r;
}
long long Dinic(int st, int en)
{
long long ret = 0;
while (bfs(st, en))
ret += dfs(st, en, 1ll << 53);
return ret;
}
int main()
{
long long tmp, sum = 0;
scanf("%d%d%d%d", &n, &m, &s, &t);
tt = n + 1;
for (int i = 1, w, x; i <= m; ++i)
{
long long y, z;
scanf("%d%d%lld%lld", &w, &x, &y, &z);
l[i] = y;
add(w, x, z - y);
flow[w] -= l[i], flow[x] += l[i];
}
for (int i = 1; i <= n; ++i)
{
if (flow[i] > 0)
{
sum += flow[i];
add(ss, i, flow[i]);
}
else if (flow[i] < 0)
add(i, tt, -flow[i]);
}
add(t, s, 1ll << 53);
if (sum == Dinic(ss, tt))
{
tmp = e[tot].val;
e[tot].val = e[tot ^ 1].val = 0;
printf("%lld\n", tmp + Dinic(s, t));
}
else
puts("please go home to sleep");
return 0;
}
|