// Touzi Mortadha
#include<bits/stdc++.h>
//Define macro functions
#define sz(a) int((a).size())
#define pb push_back
#define all(c) (c).begin(),(c).end()
#define tr(c,i) for(typeof((c).begin() i = (c).begin(); i != (c).end(); i++)
#define present(c,x) ((c).find(x) != (c).end())
#define cpresent(c,x) (find(all(c),x) != (c).end())
#define LSOne(i) (i&(-i))
#define REP(i,a,b) for(int(i)=(a);(i)<(b);i++)
#define BUG(x) {cout<<#x<<" = "<<x<<endl;}
const double epsilon = 1e-10;
using namespace std;

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> ii;
typedef long long ll;

int main()
{
    int m,p,d,s,cnt=0;
    cin>>p>>d>>m>>s;
    s-=p;
    cnt=1;
    while(s>0)
    {
        if(p>m)
            p-=d;
        if(p<=m)
            p=m;
        s-=p,cnt++;
    }
    if(s<0)cnt--;
    cout<<cnt<<endl;
    return 0;
}