#include <bits/stdc++.h>
using namespace std;
struct Node {
  int val;
  int m;
  Node* prev;
};
int n, m, k;
int a, b, c;
int x, x1, x2;
int size1, size2;
long long s;
char ch;
Node *head1, *head2;
void push(int x) {
  Node* q = new Node;
  q->val = x;
  q->prev = head1;
  if (head1 != NULL) {
    q->m = min(x, head1->m);
  }
  head1 = q;
  size1++;
}
void replace() {
  if (size2 == 0) {
    while (size1 > 0) {
      Node* q = new Node;
      q = head2->prev;
      head2 = head1;
      head1 = head1->prev;
      head2->prev = q;
      size1--;
      size2++;
    }
  }
}
void del() { head2 = head2->prev; }
int getmin() {
  if (head1 == NULL) {
    return head2->m;
  } else {
    return min(head1->m, head2->m);
  }
}
int main() {
  int n;
  double x = 0, a;
  cin >> n;
  for (int i = 0; i < n; ++i) {
    cin >> a >> a;
    x += a;
  }
  x = x / n + 5;
  cout.precision(3);
  cout << fixed << x;
  return 0;
}
