#include <bits/stdc++.h>
using namespace std;
int main() {
  float f, g, h = 0.0;
  int n;
  scanf("%d\n", &n);
  for (int i = 0; i < n; i++) {
    cin >> f >> g;
    h += g;
  }
  printf("%.3f", h / n + 5.0);
  return 0;
}
