#include <bits/stdc++.h>

using namespace std;

using ll = long long;

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    string s;
    getline(cin, s);
    int n = s.size();

    bool ans = false;
    for (int i = 0; i < n; ++i) {
        for (int j = i + 1; j < n; ++j) {
            vector<int> ban(26, false);
            for (int k = 0; k < i; ++k) {
                ban[s[k] - 'a'] = true;
            }

            for (int k = j + 1; k < n; ++k) {
                ban[s[k] - 'a'] = true;
            }

            for (int k = i; k < j + 1; ++k) {
                if ((k - i) % 2 == 1) {
                    ban[s[k] - 'a'] = true;
                }
            }

            bool f = true;
            for (int k = i; k < j + 1; ++k) {
                if ((k - i) % 2 == 0 && ban[s[k] - 'a']) {
                    f = false;
                    break;
                }
            }

            if (f) ans = true;
        }
    }
    cout << (ans ? "Yes" : "NO") << endl;
    return 0;
}