#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    long long int p,d,m,s,sum=0,cnt=0;
    long long int curr_cost;
    cin>>p>>d>>m>>s;
    curr_cost=p;
    while(sum<s){
        sum+=curr_cost;
        if(curr_cost-d>m)
            curr_cost-=d;
        else
            curr_cost=m;
        cnt++;
        //cout<<curr_cost<<endl;
    }
    if(sum>s)
    cout<<cnt-1;
    else 
        cout<<cnt;
    return 0;
}