#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 i,x=0,count=0;
    for(i=p;i<s && i>m;i=i-d)
    {
             x=x+i;
            count++;
}
for(i=x;x<s;x=x+m)
{
    x=x+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;
}