rt，不知道错哪儿

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int n, m, x, y, ans, l;
vector<int> a[1010];
bool f[1010];

bool check(int x){
  if (x == y || f[x]){
    return 0;
  }
  if (x == l){
    return 1;
  }
  f[x] = 1;
  for (int i = 0; i < a[x].size(); i++){
    if (!check(a[x][i])){
      return 0;
    }
  }
  return 1;
}

int main(){
  cin >> n >> m;
  for (int i = 0; i < m; i++){
    cin >> x >> y;
    a[x].push_back(y), a[y].push_back(x);
  }
  cin >> x >> y;
  if (check(x)){
    cout << -1;
    return 0;
  }
  for (int i = 1; i <= n; i++){
    if (i == x || i == y){
      continue;
    }
    fill(f, f + n + 1, 0);
    l = i;
    if (check(x)){
      ans++;
    }
  }
  cout << ans;
  return 0;
}