#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) {
    int i=0,len,sum=0;
   for(i=0;i<m;i++){
        p=p-d;
    sum=sum+p;
    if(sum<=s)
        len++;
   }
    if(i==m &&sum<=s){
        p=m;
    len++;
    }
return len;
}
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;
}