#include <bits/stdc++.h>
using namespace std;
const int INF = 0x7fffffff;
int main() {
  int n;
  cin >> n;
  int sum = 0;
  int zero = 0;
  for (int i = 0; i < 2 * n; i++) {
    int x;
    scanf("%*d.%d", &x);
    sum += x;
    if (x == 0) zero++;
  }
  int ans = INF;
  for (int k = 0; k <= n; k++) {
    if (k + zero < n) continue;
    ans = min(ans, abs(k * 1000 - sum));
  }
  printf("%d.%03d\n", ans / 1000, ans % 1000);
  return 0;
}
