#include <bits/stdc++.h>
using namespace std;
#define ALL(a) (a).begin(),(a).end()
#define rALL(a) (a).rbegin(),(a).rend()
typedef pair<int, int> Pint;
typedef pair<int64_t, int64_t> Pll;
typedef int64_t ll;

int main() {
    string S;
    getline(cin, S);
    set<char> A, B;
    for (int i = 0; i < S.size(); i++){
        if (i % 2 == 0){
            A.insert(S.at(i));
        }
        else {
            B.insert(S.at(i));
        }
    }
    for (int i = 0; i < 26; i++){
        char a = 'a';
        a += i;
        if (A.count(a) ^ B.count(a) && S.at(0) != a){
            cout << "Yes" << endl;
            return 0;
        }
    }
    cout << "NO" << endl;
}