#include <bits/stdc++.h>
using namespace std;
int main(int argc, char *argv[]) {
  int N;
  double sum = 0, x, y;
  scanf("%d", &N);
  for (int i = 0; i < (N); i++) {
    scanf("%lf%lf", &x, &y);
    sum += y;
  }
  printf("%.4lf\n", 5 + sum / N);
  return 0;
}
