include<iostream>

include<iomanip>

using namespace std;

int main(){ float x,a,b,c; cin>>x; a=-x+2.5; b=2-1.5(x-3)(x-3); c=x/2-1.5; if(x>0&&x<5){ cout<<fixe

#include<iostream>
#include<iomanip>
using namespace std;

int main(){
    float x,a,b,c;
    cin>>x;
    a=-x+2.5;
    b=2-1.5*(x-3)*(x-3);
    c=x/2-1.5;
    if(x>0&&x<5){
        cout<<fixed<<setprecision(3)<<a<<endl;
    }else if(x>=5&&x<10){
        cout<<fixed<<setprecision(3)<<b<<endl;
    }else if(x>=10&&x<20){
        cout<<fixed<<setprecision(3)<<c<<endl;
    }
    return 0;
}

d<<setprecision(3)<<a<<endl; }else if(x>=5&&x<10){ cout<<fixed<<setprecision(3)<<b<<endl; }else if(x>=10&&x<20){ cout<<fixed<<setprecision(3)<<c<<endl; } return 0; }