#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
int main(){
    int amount;
    int month;
    float result;
    cin>>amount>>month;
    if(amount<0){
        cout<<"Invalid input";
    }
    else if(month<1){
        cout<<"-1";
    }
    else{
        result=amount*month*0.05
        cout<<fixed<<setprecision(2)<<result;
    }
    result 0;
}