#include <bits/stdc++.h>
#define rep(i, n) for (ll i = 0; i < (n); ++i)
#define rep1(i, n) for (ll i = 1; i <= (n); ++i)
#define rrep(i, n) for (ll i = (n - 1); i >= 0; --i)
#define perm(c) sort(ALL(c));for(bool c##p=1;c##p;c##p=next_permutation(ALL(c)))
#define ALL(obj) (obj).begin(), (obj).end()
#define pb push_back
#define to_s to_string
#define len(v) (ll)v.size()
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define print(x) cout << (x) << '\n'
#define debug(x) cout << #x << ": " << (x) << '\n'
using namespace std;
using ll = long long;
typedef pair<ll, ll> P;
typedef vector<ll> vec;
typedef vector<vector<ll>> vec2;
typedef vector<vector<vector<ll>>> vec3;
ll MOD = 1e9 + 7;
ll devc(ll x, ll y) { return 1 + (x - 1) / y; }
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(20);

    string S;
    getline(cin, S);

    ll N = len(S);

    rep(i,N) rep(j,N) if(i < j){
        map<char, ll> state;
        state[' '] = 1;
        for (ll k = 0; k < i; ++k) state[S[k]] = 1;
        for (ll k = j + 1; k < N; ++k) state[S[k]] = 1;
        for (ll k = i; k <= j; ++k) if((k - i) % 2 == 1) state[S[k]] = 1;
        bool flag = true;
        for (ll k = i; k <= j; ++k) if((k - i) % 2 == 0) if(state[S[k]] == 1) flag = false;
        if(flag){
            print("Yes");
            return 0;
        }
    }

    print("NO");

    return 0;
}