Super knight

input/code.cpp: In function 'int main()':
input/code.cpp:16:22: error: 'gcd' was not declared in this scope
   16 |             mingcd = gcd(mingcd, arr[i]);
      |                      ^~~

#include <bits/stdc++.h>
using namespace std;
#define int long long
 
signed main() {
    int n, a, b;
    cin >> n >> a >> b;

    vector<int> arr(n);
    int mingcd = INT_MAX;
    for (int i = 0; i < n; i++) {
        cin >> arr[i];
        if (mingcd == INT_MAX) {
            mingcd = arr[i];
        } else {
            mingcd = gcd(mingcd, arr[i]);
        }
    }

    bool allOdd = true;
    bool allEven = true;
    for (int i = 0; i < n; i++) {
        if (arr[i] / mingcd % 2 == 0) {
            allOdd = false;
        } else {
            allEven = false;
        }
    }

    if (allOdd || allEven) {
        if (a % mingcd == 0 && b % mingcd == 0 && (a / mingcd) % 2 == (b / mingcd) % 2)
            cout << "Yes";
        else
            cout << "No";
    } else {
        if (a % mingcd == 0 && b % mingcd == 0)
            cout << "Yes";
        else
            cout << "No";
    }
}