#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 m,p,d,s;
    cin>>m>>p>>d>>s;
    int c1=m,a1=0;
    while(c1<=s)
    {
        //cout<<m<<" "<<c1<<endl;
        m = m-p;
        if(m <= d)
            m=d;
        c1 += m;
        a1++;
    }
    cout<<a1<<endl;
    return 0;
}