#include<iostream>
#include<iomanip>
using namespace std ;
int main(){
    int p ,t,r =5/100,i ;
    double ;
    cin>>p>>t;
    if(p<0||t<1){
        if(p<0){
            cout<<"Invalid input";
        }
        else if(t<1){
            cout<<"-1";
        }
    }
    else{
       i=p*t*r;
       cout<<fixed<<setprecision(2)<<i;
    }
}