#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    int principal,term;
    cin>>principal>>term;
    if(principal<0){
        cout<<"Invalid input";
    }
    else if(term <1){
        cout<<-1;
    }
    else{
        double rate=0.05;
        double interest=pricipal*rate*term/12;
        cout<<fixed<<setprecision(2)<<interest;
    }
    return 0;
}