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Liên thông mạnh
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Liên thông mạnh
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#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> ii;
typedef unsigned long long ull;
#define X first
#define Y second
#define pb push_back
#define mp make_pair
#define ep emplace_back
#define EL printf("\n")
#define sz(A) (int) A.size()
#define FOR(i,l,r) for (int i=l;i<=r;i++)
#define FOD(i,r,l) for (int i=r;i>=l;i--)
#define fillchar(a,x) memset(a, x, sizeof (a))
#define faster ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
const int N = 10005, inf = N;
int n, m, dd[N], num[N], low[N], ans;
vector<int> a[N];
stack<int> st;
void dfs(int u) {
num[u] = ++num[0];
low[u] = inf;
st.push(u);
for (auto v : a[u]) if (!dd[v]) {
if (num[v]) low[u] = min(low[u], num[v]);
else {
dfs(v);
low[u] = min(low[u], low[v]);
}
}
if (low[u] < num[u]) return;
ans++;
for (;;) {
int k = st.top();
st.pop();
dd[k] = 1;
if (k == u) return ;
}
}
int main() {
// freopen("INP.TXT", "r", stdin);
// freopen("OUT.TXT", "w", stdout);
scanf("%d%d", &n, &m);
FOR(i,1,m) {
int u, v;
scanf("%d%d", &u,&v);
a[u].ep(v);
}
FOR(u,1,n) if (!dd[u]) dfs(u);
printf("%d\n", ans);
return 0;
}