#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define sf(z) scanf("%lld",&z)
#define pf(z) printf("%lld\n",z)
#define ios ios_base::sync_with_stdio(false)
int main()
{
	ll p,d,m,s;
	cin>>p>>d>>m>>s;
	ll now=0,ans=0,cur=p;
	while(true)
	{
		now+=cur;
		if(now<=s) ans++;
		else break;
		cur=max(cur-d,m);
	}
	cout<<ans;
}