import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class Solution {
	static final boolean DEBUG = false;
	
	static void solve() {
		int p = nextInt();
		int d = nextInt();
		int m = nextInt();
		int currentMoney = nextInt();
		
		int currentCost = p;
		int bought = 0;
		while(currentMoney >= currentCost){
			bought ++;
			currentMoney -= currentCost;
			
			currentCost -=d;
			currentCost = Math.max(currentCost, m);
		}
		
		System.out.println(bought);
	}
	
	public static void main(String[] args) {
		solve();
		writer.close();
	}

	static BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
	static StringTokenizer tokenizer = new StringTokenizer("");
	static PrintWriter writer = new PrintWriter(System.out);

	static String next() {
		while (!tokenizer.hasMoreTokens())
			try {
				tokenizer = new StringTokenizer(bf.readLine());
			} catch (Exception e) {
				return null;
			}
		return tokenizer.nextToken();
	}

	static int nextInt() {
		return Integer.parseInt(next());
	}

	static long nextLong() {
		return Long.parseLong(next());
	}

	static double nextDouble() {
		return Double.parseDouble(next());
	}

	static int[] nextIntArr(int n) {
		int[] a = new int[n];
		for (int i = 0; i < a.length; i++) {
			a[i] = nextInt();
		}

		return a;
	}

}