#include<stdio.h>

int main(){

    long long p,d,m,s,i,sum=0,count=0;
    scanf("%lld %lld %lld %lld",&p,&d,&m,&s);
    for(i=p;i>=m;i-=d){
        if(sum>s){
            printf("%lld",count-1);
            return 0;
        }
        sum+=i;
        count++;
    }
    count+=(s-sum)/m;
    printf("%lld",count);
    return 0;
}