#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 p,d,m,s;
    cin>>p>>d>>m>>s;
    
    long long int ans = 0;
    long long int count = 0;
    while(ans<=s){
        ans+=p;
        count++;
        if(p-d>=m){
            p-=d;
        }else{
            p = m;
        }
    }
    cout<<--count;
    return 0;
}