#include <bits/stdc++.h>

using namespace std;

#define N 110

int dl, dw, g, l;
double dp[N][N];

int main()
{
    scanf("%d%d%d%d", &dl, &dw, &g, &l);
    dp[0][0] = 1;
    double ans = 0;
    for (int i = 1; i <= 100; i++)
    {
        for (int j = 0; j <= 100; j++)
        {
            dp[i][min(100, j + dl)] += dp[i - 1][j] * l / 100.;
            dp[i][min(100, j + dw)] += dp[i - 1][j] * (1. - l / 100.) * (1. - j / 100.);
            ans += dp[i - 1][j] * (1. - l / 100.) * j / 100. * i;
        }
    }
    if (l != 0)
        ans += dp[100][100] * l / 100. * (10100. / l + 100. / (100. - l));
    printf("%.12f\n", ans * 100. / g);
    return 0;
}