#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,r=0;
    std::cin>>p>>d>>m>>s;
    while(s>=p){
        s-=p;
        p=std::max(m,p-d);
        ++r;
    }
    std::cout<<r<<std::endl;
    return 0;
}