#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    int p,d,m,money,sum=0,max=0;
    cin>>p>>d>>m>>money;
    while(sum<(money-p+1)){
        sum=sum+p;
        if(p>(m+d-1))
        { p-=d;
        ++max;
           }
        else 
        {p=m;++max;}
    }
           cout<<max;
           return 0;
}