Untitled

#include <bits/stdc++.h>
using namespace std;
#define ll long long
int tt, tc;

int tiles[7][7], n;
pair<int, int> given[28];

pair<int, int> norm(int a, int b) {
    if (a > b) swap(a, b);
    return make_pair(a, b);
}

int dp[28][7][7];

int valid(int i, int x, int y) {
    if (i == n) {
        for (int j = 0; j < 7; j++)
            for (int k = 0; k < 7; k++) if (!tiles[j][k]) {
                if (j == x || j == y || k == x || k == y) return 1;
            }
        return 0;
    }
    int& ret = dp[i][x][y];
    if (ret != -1) return ret;

    int a = given[i].first, b = given[i].second;
    vector<pair<int, int>> to_states;
    if (a == x) to_states.push_back(norm(b, y));
    if (a == y) to_states.push_back(norm(b, x));
    if (b == x) to_states.push_back(norm(a, y));
    if (b == y) to_states.push_back(norm(a, x));
    sort(to_states.begin(), to_states.end());
    to_states.erase(unique(to_states.begin(), to_states.end()), to_states.end());

    assert((int)to_states.size() <= 2);
    ret = 0;
    for (auto& [xx, yy] : to_states) ret = ret | valid(i + 1, xx, yy);
    return ret;
}

void solve() {
    memset(dp, -1, sizeof(dp));
    cin >> n;

    for (int i = 0; i < n; i++) {
        cin >> given[i].first >> given[i].second;
    }
    for (int i = 0; i < n; i++) {
        int x = given[i].first, y = given[i].second;
        tiles[x][y] = tiles[y][x] = 1;
    }
    if (n == 1) {
        cout << "Yes\n";
        return;
    }
    auto p = norm(given[0].first, given[0].second);
    cout << (valid(1, p.first, p.second) ? "Yes\n" : "No\n");
}

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	tt = 1, tc = 1;
	// cin >> tt;
	while (tt--) {
		solve();
		tc++;
	}
}