#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 p,d,m,s;
    cin>>p>>d>>m>>s;
    long sum=p,cnt=0;
    while(sum<=s)
    {   
        p=p-d;
        if(p<m)
            break;
        sum=sum+p;
        //cout<<p<<" ";
        cnt++;
    }
    if(sum<s)
    {
        while(sum<=s)
        {
            sum=sum+m;
            cnt++;
        }
    }
    cout<<cnt;
    return 0;
}