#include <bits/stdc++.h>
#define rep(i,n) for (int i=0; i<(n); ++i)
using namespace std;
using ll=long long;
int main(){
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    int ans=0;
    int cnt=1+c;
    while(cnt<d){
        ans++;
        cnt+=1+c;
    }
    cout<<ans<<endl;
}