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