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

int count =0;
int howManyGames(int p, int d, int m, int s) {
    // Return the number of games you can buy
    while(s>m)
    {
        if(s-d*count>m)
            s-=p-d*count;
        else
            s-=m;
            count++;
    }
    return count;
}

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;
}