C++ :

#include <iostream>
#include <cmath>
using namespace std;

int main() {
    string binary = "";
    cin >> binary;

    int decimal = 0;
    int length = binary.length();

    for (int i = 0; i < length; i++) {
        if (binary[length - 1 - i] == '1') {
            decimal += pow(2, i);
        }
    }
    cout << decimal << endl;
    return 0;
}