#include<bits/stdc++.h>
using namespace std;

int main(){
    int p,d,m,s,n=0;
    cin>>p>>d>>m>>s;
    while(s>=p && p>m){
        s-=p;
        p-=d;
        n++;
    }
    if(p<=m)
    n=n+(s/(double)m);
    cout<<n;
}