#include <bits/stdc++.h>
using namespace std;


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