#include <iostream>
#include <cstdio>
using namespace std;
int main(int argc, char** argv) {
	double a,b,c,d;
	cin >> a >> b >> c >> d;
	printf("%.10lf",(c-a)/(b+d)*b+a);
	return 0;
}
/*Jai Shree Ram*/
// Never Give Up
#include<bits/stdc++.h>
#include<unordered_map>
using namespace std;
 
#define ff              first
#define ss              second
#define int             long long
#define pb              push_back
#define mp              make_pair
#define pii             pair<int,int>
#define vi              vector<int>
#define mii             map<int,int>
#define umii            unordered_map<int,int>
#define pqb             priority_queue<int>
#define pqs             priority_queue<int,vi,greater<int> >
#define setbits(x)      __builtin_popcountll(x)
#define zrobits(x)      __builtin_ctzll(x)
#define mod             1000000007
#define inf             1e18
#define ps(x,y)         fixed<<setprecision(y)<<x
#define mk(arr,n,type)  type *arr=new type[n];
#define w(x)            int x; cin>>x; while(x--)
#define F(i,s,e,j)        for(int i=s;i<=e;i+=j)
#define mt19937                 rng(chrono::steady_clock::now().tjhe_since_epoch().count());   
//shuffle(arr,arr+n,rng)
 void c_p_c()
{
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
}
int dp[16][1<<8][9][17];
int total_ways(int idx,int j,int mask1,int mask2,int n,int a,int b)
{
	if(idx==-1)
			return  mask1==0?1:0;
		
	if(j==0 && dp[idx][mask1][a][b]!=-1)
      return dp[idx][mask1][a][b];
	if(j==n)
	return total_ways(idx-1,0,mask2,0,n,a,b);
	if(mask1&(1<<j))
		return total_ways(idx,j+1,mask1,mask2,n,a,b);
	int ans = 0;
    if(j<n-1 && (mask1&(1<<(j+1)))==0 && a>0)
    	ans += total_ways(idx,j+2,mask1,mask2,n,a-1,b);
     if(idx>=1 && a>0)
       ans += total_ways(idx,j+1,mask1,mask2|(1<<j),n,a-1,b);
    if(b>0)
       ans += total_ways(idx,j+1,mask1,mask2,n,a,b-1);
    return dp[idx][mask1][a][b] = ans;
}
int32_t main()
{   c_p_c();
    int n,m,a,b;
    cin>>n>>m>>a>>b;
    memset(dp,-1,sizeof(dp)); 
    cout<<total_ways(m-1,0,0,0,n,a,b)<<endl;
}