#include <bits/stdc++.h>
using namespace std;
double x;
double ans;
void f(double x){
    if(x >= 0 && x < 5) ans = x - 2 * abs(x) + 2.5;
    else if(x >= 5 && x < 10) ans = 2 - 1.5 * (x - 3.0) * (x - 3.0);
    else if(x >= 10 && x < 20) ans = x / 2.0 - 1.5;
}
int main(){
    scanf("%1ld",x);
    f(x);
    printf("%3ld",x);
    return 0;
}