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