#include <iostream>
#include<stdio.h>
#include<sstream>
#include<bits/stdc++.h>
#include<stdio.h>
#include<vector>
#include<map>
#include<queue>
#include<math.h>
#include<list>
#include<limits.h>
#include<algorithm>
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define present(container, element) (container.find(element) != container.end())
#define cpresent(container, element) (find(all(container),element) != container.end())
#define all(c) c.begin(), c.end()
#define MOD 1000000007
#define MAX 10000
typedef long long ll;
using namespace std;
int main()
{
ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    ll n,m,t,x,a,b,s,d,p;
    cin>>p>>d>>m>>s;
    ll count=0;
    s-=p;
while(1){
    if(s>=0){
        count++;
    }
    else break;
    p-=d;
    if(p<=m){
        p=m;
    }
    s-=p;
    
}
cout<<count;
    return 0;
}