func_code_string: #include <bits/stdc++.h>   int n, m;   int a[2000];   int b[2000];   int can[2000];   using namespace std;   int main() {     int c = 0;     cin >> n;     for (int i = 0; i < n; i++) {       cin >> a[i] >> b[i];     }     for (int i = 0; i < n; i++) {       for (int j = 0; j < n; j++) {         if (i != j && !can[j] && b[i] == a[j]) {           can[j] = 1;           c++;         }       }     }     cout << n - c << endl;   }   