HDU 2401.Baskets of Gold Coins

#include <iostream>
#include <algorithm>
#include <stdio.h>
#include <vector>
#include <queue>
#include <map>
#include <math.h>
#include <string>
#include <string.h>
#include <bitset>

#define INF 0xfffffff
#define MAXN 100105

using namespace std;

int n,w,d,x;

int main(){
while(scanf("%d%d%d%d",&n,&w,&d,&x)!=EOF){
int y = (n-1)*n*w/2-x;
if(y==0)cout<<n<<endl;
else cout<<y/d<<endl;
}
}