#include<bits/stdc++.h>
using namespace std;
#define ll long long
int main()
{
    ll t,n,p,d,m,s,sum=0,cnt=0,k;
    cin>>p>>d>>m>>s;
    while(1)
    {
        if(sum==s)
        {
            cout<<cnt;
            break;
        }
        else if(sum>s)
        {
            cout<<cnt-1;
            break;
        }
        sum+=p;
       // cout<<sum<<endl;
        if(p-d<m)
        {
            p=m;
        }
        else
            p=p-d;
        cnt++;
    }
}