text: #include <bits/stdc++.h>
  using namespace std;
  
  int n, full;
  long long eat;
  
  int read() {
      int ret, flag = 1;
      char ch;
      while(!isdigit(ch = getchar())) (ch == '-') && (flag = -1);
      for(ret = ch - '0'; isdigit(ch = getchar()); ret *= 10, ret += ch - '0');
      return ret * flag;
  }
  
  void print(int x) {
      if(x < 0) { putchar('-'); x *= -1; }
      if(x > 9) { print(x / 10); }
      putchar(x % 10 + '0');
  }
  
  int main() {
      n = read();
      for(int i = 1; i <= n; ++i) {
          int tmp = read();
          if(tmp >= 1) ++full, eat += tmp;
      }
      printf("%lf\n", (double)(eat) / (double)(full) * (double)(eat));
      return 0;
  }