45分求助

#include<bits/stdc++.h>
#define db double
using namespace std;
db n,m,x,y,u,z;
int main(){
	cin>>n>>m>>x>>y;
	if(y>n)	u=y-m;
	z=y*x/10;
	printf("%.2f",min(u,z));
	return 0;
}