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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int p,d,m,s,sum=0,c=0;
    cin>>p>>d>>m>>s;
    
    while(sum<=s)
    {
        if(p>s)
            break;
        if(sum==0)
        {
            sum+=p;
            c++;
        }
        else
        {
            if(p>=m)
            {      p-=d;
                   if(p<m)
                   p=m;
            }
            else
                p=m;
            sum+=p;
            if(sum<=s)
            c++;
        }
        
    }
    cout<<c;
    
    return 0;
}