#include <bits/stdc++.h>
using namespace std;
#define lets_do_this ios_base::sync_with_stdio(false);cin.tie(NULL);
struct cell{string s;int index;};
bool op(const cell &a,const cell &b)
{
    return (a.s < b.s);
}

int main() {
    lets_do_this
    long long n,p,d,m,s;
    cin>>p>>d>>m>>s;
    long sum = 0,countt = 0;
    while(sum < s)
    {
        
        {
        sum+=p;
        countt++;}
        if(p > m)
        p-=d;
        if(p < m)
        p = m;
    }
    if(sum > s)
    {
        if(countt)
        cout<<countt-1;
        else cout<<0;
    }
    if(sum<=s)cout<<countt;
    //cout<<
    vector<cell>Vcell;
    vector<long long >Vll;
    vector<long >Vl;
    vector<int >Vi;
}