#include<bits/stdc++.h>

using namespace std;
#define foreach(i,x) for(type(x)i=x.begin();i!=x.end();i++)
#define FOR(ii,aa,bb) for(int ii=aa;ii<=bb;ii++)
#define ROF(ii,aa,bb) for(int ii=aa;ii>=bb;ii--)
#define type(x) __typeof(x.begin())

#define bit(x,y) ((x>>y)&1)
#define y1 fkfrgff
#define ll long long
#define pii pair<int,int>
#define mod 1000000007
#define N (int)(1e6+10)
#define mp make_pair
#define pb push_back
#define sd second
#define ft first
#define endll puts("")
#define endl '\n'
#define inf mod

int ss,p,d,s,m,cur;
int main(){
        scanf("%d %d %d %d",&p,&d,&m,&s);
cur = p;
        while(s >= 0){
                s-=cur;
                cur -= d;
                cur = max(cur,m);
if(s >= 0)
ss++;
        }
cout << ss << endl;
}