#include <iostream>
#include <bits/stdc++.h>
using namespace std;
typedef long double ld;
typedef long long ll;

#define fi first
#define sc second
#define EPS 1e-9
double  g,p;
int dw,dl;
double dp[105];
int vis[105];
double solve(int cur)
{
    if(cur==100)return 100.0/(100.0-p);
    if(vis[cur])return dp[cur];
    vis[cur]=1;
    dp[cur]=1+solve(min(100,cur+dl))*p/100.0+solve(min(100,cur+dw))*((100.0-cur)/100)*((100.0-p)/100.0);
    return dp[cur];
}
int main()
{
	ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	cin>>dl>>dw>>g>>p;
	cout<<fixed<<setprecision(10);
	cout<<solve(0)*100.0/g;
	return 0;
}
/*5
-1 1
1 2
-1 3
2 6
3 5


5 2
.##..
.#.#.
.....
#....
###..
*/