60求调

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<set>
using namespace std;
double x,y,n,p,cnt1,cnt2,minn=999999999;
int main()
{
	cin>>x>>y>>n>>p;
	if(p>=x) cnt1=p-y;
	cnt2=p/10*n;
	minn=min(cnt1,cnt2);
	printf("%.2lf",minn);
	return 0;
}