84分，求大佬帮下

B2047

#include<bits/stdc++.h>
using namespace std;
double fenduan(double x)
{
    if(x<=5) return -x+2.5;
    else if(x<10) return 2-1.5*(x-3)*(x-3);
    else if(x>=10) return x/2-1.5;
    else return 0;
}
int main(){
    double x;
    cin>>x;
    double y=fenduan(x);
    printf("%.3lf",y);
    return 0;
}