#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include <stdbool.h>

int howManyGames(int p, int d, int m, int s) {
    // Return the number of games you can buy
    //if(p > s){
      //  return 0;
    //}
    int num = 1, value = p - d, cost = p;
    int n = (p - m) / d + 1, iter = 1;
    while(cost < s && iter != n){
        num++;
        cost += value;
        value -= d;
        iter++;
    }
    if(cost > s){
        return num - 1;
    }
    else if(cost == s){
        return num;
    }
    else{
        while(cost < s){
            cost += m;
            num ++;
        }
        if(cost > s){
            return num - 1;
        }
        else return num;
    }
}

int main() {
    int p; 
    int d; 
    int m; 
    int s; 
    scanf("%i %i %i %i", &p, &d, &m, &s);
    int answer = howManyGames(p, d, m, s);
    printf("%d\n", answer);
    return 0;
}