#include <array>
#include <iostream>
#include <vector>

using namespace std;

int main() {
  int n;
  cin >> n;
  vector<array<int, 2>> v(n);
  for(auto& x: v) {
    cin >> x[0] >> x[1];
    x[0]--; x[1]--;
  }
  int ret = 0;
  for(int i = 0; i + 2 < n;) {
    if(v[i][1] >= i+2 && v[i+2][0] <= i) {
      ret++;
      i += 3;
    }
    else i++;
  }
  cout << ret << "\n";
}