#include <iostream> using namespace std; int main(){ double x,y; cin>>x; if(0<=x&&5>x) printf("%.3f",-x+2.5); if(5<=x&&x>10) printf("%.3f",-x+2.5); if(10<=x&&x>15) printf("%.3f",-x+2.5); if(15<=x&&x>20) printf("%.3f",-x+2.5); return 0; }