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NUMBER.cpp
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NUMBER.cpp
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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 = 1e4+5;
int n, m, t, low[N], num[N];
int in[N], degOut[N], T;
vector<int> a[N];
stack<int> st;
bool dd[N][N];
void dfs(int u) {
num[u] = ++num[0];
low[u] = n+1;
st.push(u);
for (auto v : a[u]) {
if (in[v]) continue;
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 ;
++m;
for (;;) {
int v = st.top();
st.pop();
in[v] = m;
if (v == t) T = m;
if (v == u) break;
}
}
int main() {
// freopen("INP.TXT", "r", stdin);
// freopen("OUT.TXT", "w", stdout);
scanf("%d%d%d", &n,&m,&t);
while (m--) {
int i, j;
scanf("%d%d", &i,&j);
a[i].pb(j);
}
m = 0;
FOR(i,1,n) if (!in[i]) dfs(i);
FOR(i,1,n) {
for (auto j : a[i]) {
int u = in[i], v = in[j];
if (u == v || dd[u][v]) continue;
dd[u][v] = 1;
degOut[u]++;
}
}
int ans = 0;
FOR(i,1,m) ans += degOut[i] == 0 && i != T;
printf("%d\n", ans);
return 0;
}