#include <bits/stdc++.h> using namespace std; int n; int nxt[100000]; string p[100000]; map<string, int> mp; inline void Subtask1() { vector<int> f; f.resize(1 << n, 1e9); f[0] = 0; for (int i = 0; i < (1 << n); ++i) { if (__builtin_popcount(i) & 1) { continue; } for (int j = 0; j < n; ++j) { for (int k = j + 1; k < n; ++k) { if (((i >> j) & 1) && ((i >> k) & 1)) { f[i] = min(f[i], (nxt[j] != k) + (nxt[k] != j) + f[i - (1 << j) - (1 << k)]); } } } } cout << f[(1 << n) - 1]; } int main() { ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); cin >> n; for (int i = 0; i < n; ++i) { cin >> p[i]; mp[p[i]] = i; cin >> p[i]; } for (int i = 0; i < n; ++i) { nxt[i] = mp[p[i]]; } if (n & 1) { cout << -1; return 0; } Subtask1(); return 0; }