func_code_string: #include <bits/stdc++.h>   using namespace std;   int fen[100100];   int n, ans = -1, a[100100];   int calc(int ind) {     int ans = 0;     for (int i = ind; i >= 1; i -= i & (-i)) ans ^= fen[i];     return ans;   }   int main() {     ios::sync_with_stdio(false);     cin.tie(0);     cout.tie(0);     ;     memset(fen, 0, sizeof(fen));     cin >> n;     for (int i = 2; i <= n; i++) {       int t;       int p = 0;       set<int> s;       for (int j = 2; j * (j + 1) / 2 <= i; j++) {         int k = i - j * (j + 1) / 2;         if (k % j != 0) continue;         k /= j;         t = calc(k + j) ^ calc(k);         if (i == n and ans == -1 and !t) ans = j;         s.insert(t);       }       while (s.count(p)) p++;       for (int j = i; j <= n; j += j & (-j)) fen[j] ^= p;     }     cout << ans;     return 0;   }   