#include <iostream>

int fromBin(int n)
{
    int factor = 1;
    int total = 0;

    while (n != 0)
    {
        total += (n%10) * factor;
        n /= 10;
        factor *= 2;
    }

    return total;
}

int main() {
	std::cout << fromBin(101) << std::endl;
	return 0;
}