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


int main() {
     int ans=0,p,d,m,s;
    cin>>p>>d>>m>>s;
    while(true)
    {
    	s-=p;
    	if(s<0)
    		break;
    	ans++;
    	p-=d;
    	if(p<m)
    		p = m;
    }
    cout<<ans<<endl;
  
    return 0;
}