#include <bits/stdc++.h>
using namespace std;
const int N = 5e6 + 5;
const long long inf = 1791791791;
const long long mod = 1e9 + 7;
int main() {
  int n;
  scanf("%d", &n);
  double resp = 0;
  for (int i = 0; i < n; i++) {
    double b;
    scanf("%*lf %lf", &b);
    resp += b;
  }
  printf("%lf\n", 5.0 + resp / (double)n);
  return 0;
}
