#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ long long x,y; cin>>x; if(x<5) { cout<<-x+2.5; } else if(x<10) { cout<<2-1.5*(x-3)*2; } else { cout<<x/2-1.5; } printf("%.3lf",y); return 0; }