#include <iostream>

#include <cstring>

#include <cstdio>

#include <algorithm>

#include <cmath>

#include <map>

#include <vector>

using namespace std;

typedef long long ll;

typedef unsigned long long ull;

const int N =10001;

vector<int>prime;

int pri[N];

int num[N];

void getprime()

{

    memset(pri,1,sizeof(pri));

    for(int i = 2; i <= N; i++)

    {

        if(pri[i])

        {

            prime.push_back(i);

            for(int j = i+i; j <= N; j+=i)

                pri[j] = 0;

        }

    }

}

void add_factorial(int n,int d)   //

{

    for(int i = 1;i <= n;i++)

    {

        int tt = i;

        for(int j = 0;j < prime.size();j++)

        {

            while(tt % prime[j] == 0)

            {

                num[j]+=d;

                tt /= prime[j];

            }

            if(tt == 1)

                break;

        }

    }

}

int main()

{

    int p,q,r,s;

    getprime();

    while(scanf("%d%d%d%d",&p,&q,&r,&s) != EOF)

    {

        memset(num,0,sizeof(num));

        add_factorial(p,1);

        add_factorial(q,-1);

        add_factorial(p-q,-1);

        add_factorial(r,-1);

        add_factorial(s,1);

        add_factorial(r-s,1);

        double ans = 1.0;

        for(int i = 0;i < prime.size();i++)

        {

            ans *= pow(prime[i],num[i]);

        }

        printf("%.5lf\n",ans);

    }

    return 0;

}