#include <bits/stdc++.h>
using namespace std;
float x, y, s = 0;
int n;
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> x >> y;
    s += y;
  }
  s = s / n;
  printf("%.3f", s + 5);
  cout << endl;
  return 0;
}
