#include<bits/stdc++.h>
#include <algorithm>    // std::is_sorted, std::prev_permutation

using namespace std;
#define ll long long int
#define mo 100000007
int main()
{


    ll p,d,m,s,i,cnt;
    cin>>p>>d>>m>>s;
    std::vector<ll> v;
    v.push_back(p);
    ll su=p;
    if(p>s){
    	cout<<"0\n";
    }
    else{
    	cnt=1;
	    for(i=1;;i++){
	    	if((v[i-1]-d)<m)
	    		v.push_back(m);
	    	else
	    		v.push_back(v[i-1]-d);
	    	su+=v[i];
	    	if(su>s)
	    		break;
	    	else
	    		cnt++;
	    }
	        cout<<cnt<<"\n";

    }
    

  /*  for(i=0;i<v.size();i++){
    	cout<<v[i]<<endl;

    }*/
 }