#include<bits/stdc++.h>
using namespace std;
int main(){
long long int p,d,m,s,t,c=0;
    cin>>p>>d>>m>>s;
    t=0;
    while(t<=s){
        t=t+p;
        p=p-d;
        if(p<m)
            p=m;
        c++;
    }
    cout<<c-1;
return 0;
}