#pragma GCC optimize("Ofast")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")

#include "bits/stdc++.h"

#define int long long
#define rep(i, n) for(int (i)=0 ;(i)<n ;(i)++)
using namespace std;
#define double long double
const int N = 10000;
double dp[N];
double deltaL, deltaW, probOfG, probofL, W;
double zby1;

double solve(int curProb) {
    if (curProb >= 100)return 1 / W;
    double &cur = dp[curProb];
    if (cur > -1)return cur;
    cur = 0;
    return cur = 1 + W * ((100 - curProb) / 100.0 * solve(curProb + deltaW)) + probofL * solve(curProb + deltaL);
}

signed main() {
    for (int i = 0; i < N; i++)
        dp[i] = -1;
    cin >> deltaL >> deltaW >> probOfG >> probofL;
    probofL /= 100;
    probOfG /= 100;
    W = 1 - probofL;

    cout << fixed << setprecision(9) << solve(0) / probOfG << endl;
}