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


int main() {
    
    int p,d,m,s,sum=0,c=0;
    cin>>p>>d>>m>>s;
    
    int i=p;
    while(sum<=s)
    {
        sum+=i;
        
        i=i-d;
        if(i<m)
            i=m;
        
        c++;
    }
    
    cout<<c-1;
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    return 0;
}