B. Archer
time limit per test
memory limit per test
input
output
SmallR is an archer. SmallR is taking a match of archer with Zanoes. They try to shoot in the target in turns, and SmallR shoots first. The probability of shooting the target each time is
for SmallR while
for Zanoes. The one who shoots in the target first should be the winner.
Output the probability that SmallR will win the match.
Input
A single line contains four integers
.
Output
Print a single real number, the probability that SmallR will win the match.
10 - 6.
Sample test(s)
input
1 2 1 2
output
0.666666666667
等比数列无限求和公式 a+ap+ap^2+... 0<p<1 --> S=a/(1-p)
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<functional>
#include<cmath>
#include<cctype>
using namespace std;
#define For(i,n) for(int i=1;i<=n;i++)
#define Rep(i,n) for(int i=0;i<n;i++)
#define Fork(i,k,n) for(int i=k;i<=n;i++)
#define ForD(i,n) for(int i=n;i;i--)
#define Forp(x) for(int p=pre[x];p;p=next[p])
#define RepD(i,n) for(int i=n;i>=0;i--)
int main()
{
// freopen(".in","r",stdin);
// freopen(".out","w",stdout);
double a,b,c,d;
cin>>a>>b>>c>>d;
printf("%.12lf\n",a/b/(1-(1-a/b)*(1-c/d)));
return 0;
}
