#include<bits/stdc++.h>
#define ll long long int
using namespace std;

int main()
{
    int p,d,s,m;
    ll c=0,sum=0,val;
    cin>>p>>d>>m>>s;
    sum+=p;
    val=p;
    while(sum<=s && val>=m)
    {
        val-=d;
        if(val<m)
            val=m;
        sum+=val;
        c++;
    }
    cout<<c<<endl;
    return 0;
}