#include<stdio.h>
int main()
{
    int n,d,b,s,c=0;
    scanf("%d%d%d%d",&n,&d,&b,&s);
    while(s>=n)
    {
        s-=n;
        c++;
        if(n>b)
            n-=d;
        if(n<b)
            n=b;
    }
    printf("%d",c);
}