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


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