#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define all(x) x.begin(),x.end()
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define rep_r(i,a,b) for(int i=a;i>=b;i--)
#define each(a,x) for (auto& x : a)
using pi = pair<int,int>;
using pl = pair<ll,ll>;
using vi = vector<int>;
using vl = vector<ll>;
#define fi first    
#define se second
#define sz(x) int(x.size())
#define so(x) sort(all(x))
#define so_r(x) sort(all(x),greater<int>())
#define zero(x) memset(x,0,sizeof(x))
#define pb push_back
#define lb lower_bound
#define ub upper_bound
const char nl = '\n';
int dx[4] = {1,-1,0,0};
int dy[4] = {0,0,1,-1};
int bit_cnt(int x){
    return __builtin_popcount(x);
}
ll bex(ll a, ll b, ll mod = 1e9 + 7){ll res = 1LL; while(b){ if (b&1) res = res * a % mod; a = a * a % mod; b >>= 1;} return res;}
template<class t,class u> bool chmax(t&a,u b){if(a<b){a=b;return true;}else return false;}
template<class t,class u> bool chmin(t&a,u b){if(b<a){a=b;return true;}else return false;}

// armistcxy
const int MOD = 1e9 + 7; // 998244353
const int N = 1e5 + 5;
const ll INF = 1e18;

void solve(){
    int v1, v2; cin >> v1 >> v2;
    double d,w; cin >> d >> w;
    double t = 0;
    while (d > 1e-6){
        double cur = d / (w + v2);
        d -= cur * (v1 + v2);
        t += cur;
    }
    cout << fixed << setprecision(6);
    cout << t * w << nl;
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int t = 1; //cin >> t;
    while (t--){
        solve();
    }
}