include<stdio.h>

int main() { int n1; float n2,n3; scanf("%d%f",&n1,&n2); if(n1>0&&n2>=0) { if(n2<=2000&&n1<=2000) { if(n1%5==0&&n1<n2) { n3=n2-n1-0.5; printf("\n%.2f\n",n3); } } } else printf("\n%.2f\n",n2);

return 0; }