#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 */ 
    long long int c=-1,p,d,m,s;
    cin>>p>>d>>m>>s;
    while(s>=0)
    {
            s=s-p;
        if((p-d)>m)
            p=p-d;
        else
            p=m;
            c++;
    }
    cout<<c<<endl;
    return 0;
}