#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
    
    int j,k,c=-2,y=0,r=0;
    
    while(p>m)
    {   
        j=p;
        k=s;
        p=p-d;
        s=s-p;
        c++;
    }
    
    y=(k-j)/m;
    
    r=y+c;
    
    return r;
}

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;
}