65pts 求条

#include <iostream>
using namespace std;
double x,y,n,p;
int main(){
    cin>>x>>y>>n>>p;
    int f;
    if(p>=x)f=p-y;
    double d=p/10*n;
    if(f>d)printf("%.2lf",d);
    else printf("%.2lf",f);
    return 0;
}