P3802 小魔女帕琪

 

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<queue>
#include<vector>
#include<bits/stdc++.h>
#define ll long long
#define ddd printf("----------------------\n");
using namespace std;
const int maxn=1e1 ;

int a[10],n;
double ans=1;

int main()
{
    ios::sync_with_stdio(false);
    for(int i=1;i<=7;i++) cin>>a[i],n+=a[i];
    if(n<=6){ cout<<"0.000"<<'\n';return 0;}
    
    for(int i=1;i<=7;i++) ans=(double) ans*a[i]*i/(n-i+1);
    ans=(double)ans*(n-6);
    printf("%.3lf\n",ans);
    
    
    
    
    
    return 0;
}