#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 price, diff, max, cash, cost=0 , result=-1;
    cin>>price>>diff>>max>>cash;
    while(cost <= cash){
        result++;
        cost= cost+price;
        if(price-diff > max){
            price = price-diff;
        }
        else
            price = max;
    }
    cout<<result;
    return 0;
}