#include <bits/stdc++.h>
using namespace std;
int main() {
  int b, c, i, j, k = 0, m[1000][1000] = {0};
  for (i = 0; i < 6; i++) {
    cin >> b >> c;
    m[b][c]++;
    m[c][b]++;
  }
  for (i = 0; i < 1000; i++) {
    c = 0;
    for (j = 0; j < 1000; j++) {
      c += m[i][j];
    }
    if (c % 4) k++;
  }
  if (k)
    cout << "no" << endl;
  else
    cout << "yes" << endl;
  return 0;
}
