按题意直接模拟即可。

AC code：

// Paste your Program A here
#include <bits/stdc++.h>
using namespace std;

int main() {
    string S;
    cin >> S;
    int X = 0;
    for (int i = 0; i < S.size(); ++i) {
        if (S[i] == '1') {
            X ^= (i + 1);
        }
    }
    
    cout << X << endl;
    return 0;
}

/* ATTENTION!!! THIS IS THE BARRIER!!! */

// Paste your Program B here
#include <bits/stdc++.h>
using namespace std;

int main()
{
    string T;
    int X;
    cin >> T >> X;
    int D = 0;
    int t_xor = 0;
    for (int i = 0; i < T.size(); ++i) {
        if (T[i] == '1') {
            t_xor ^= (i + 1);
        }
    }
    int diff = X ^ t_xor;
    if (diff > 0 && diff <= T.size()) {
        D = diff;
    }
    cout << D << endl;
    return 0;
}