[期望]洛谷 P3802 小魔女帕琪

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
double Out,a[10],ans;

int main(){
    cin>>a[1]>>a[2]>>a[3]>>a[4]>>a[5]>>a[6]>>a[7];
    ans = a[1]+a[2]+a[3]+a[4]+a[5]+a[6]+a[7];
    Out = 5040 * a[1]/ans * a[2] /(ans-1) * a[3] /(ans-2) * a[4] /(ans-3) * a[5] /(ans-4) * a[6] /(ans-5) * a[7]; 
    printf("%.3lf",Out);
    return 0;
}