#include <bits/stdc++.h>
 
using namespace std;
 
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef pair<ld,ld> pdd;
 
typedef pair<int, ull> piu;
typedef pair<ull, int> pui;
 
#define X first
#define Y second

namespace io{
	const int L = (1 << 20) + 1;
	
	char buf[L], *S , *T, c;
	 
	char getchar() {
		if(S == T) {
			T = (S = buf) + fread(buf, 1, L, stdin);
			return (S == T ? EOF : *S++);
		}
		return *S++;
	}
	
	int inp() {
		int x = 0, f = 1; char ch;
		for(ch = getchar(); !isdigit(ch); ch = getchar())
			if(ch == '-') f = -1;
		for(; isdigit(ch); x = x * 10 + ch - '0', ch = getchar());
		return x * f;
	}
	
	ll inp_ll() {
		ll x = 0; int f = 1; char ch;
		for(ch = getchar(); !isdigit(ch); ch = getchar())
			if(ch == '-') f = -1;
		for(; isdigit(ch); x = x * 10 + ch - '0', ch = getchar());
		return x * f;
	}
	
	ull inp_ull() {
		ull x = 0; char ch;
		for(ch = getchar(); !isdigit(ch); ch = getchar());
		for(; isdigit(ch); x = x * 10 + ch - '0', ch = getchar());
		return x;
	}
	
	void inp_str(char *s)
	{
		int len = 0;
		char ch;
		for (ch = getchar(); !isdigit(ch); ch = getchar());
		for (; isdigit(ch); ch = getchar())
			s[len ++] = ch;
		s[len] = 0;
	}
	
	char B[25], *outs=B+22, *outr=B+22;
	template<class T>
	inline void print(register T a,register char x=0){
		if(x) *--outs = x, x = 0;
		
		if(!a)*--outs = '0';
		else 
			while(a)
				*--outs = (a % 10) + 48, a /= 10;
		
		fwrite(outs, outr - outs , 1, stdout);
		outs = outr;
	}
};
 
using io :: print;
using io :: inp;
using io :: inp_ull;
using io :: inp_str;

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