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