题解

#include <iostream>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int k;
    cin >> k;
    if (k <= 1) {
        cout << "Yes" << endl;
        return 0;
    }
    char prev_c;
    int prev_num;
    cin >> prev_c >> prev_num;
    for (int i = 1; i < k; ++i) {
        char curr_c;
        int curr_num;
        cin >> curr_c >> curr_num;
        if (curr_c == prev_c) {
            cout << "No" << endl;
            return 0;
        }
        
        prev_c = curr_c;
    }
    cout << "Yes" << endl;
    return 0;
}