#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rrep(i, n) for (int i = (int)(n - 1); i >= 0; i--)
#define all(x) (x).begin(), (x).end()
#define sz(x) int(x.size())
#define get_unique(x) x.erase(unique(all(x)), x.end());
typedef long long ll;
typedef complex<double> Complex;
const int INF = 1e9;
const ll LINF = 1e18;
const ll MOD = 998244353;
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;
}
template <class T>
vector<T> make_vec(size_t a) {
    return vector<T>(a);
}
template <class T, class... Ts>
auto make_vec(size_t a, Ts... ts) {
    return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

int main() {
    string s;
    getline(cin, s);
    for (char& c : s)
        if (c == ' ') c = '.';
    vector<bool> v(26);
    int n = sz(s);
    for (int i = 1; i < n; i += 2) {
        if (s[i] != '.') {
            v[s[i] - 'a'] = 1;
            s[i] = '.';
        }
    }

    for (char& c : s)
        if (c != '.' && v[c - 'a']) c = '.';

    int l = 0, r = n - 1;
    while (l < n && s[l] == '.') l++;
    while (r - 1 >= 0 && s[r - 1] == '.') r--;
    // cout << s << " " << l << " " << r << endl;
    if (r <= l) {
        cout << "NO" << endl;
        return 0;
    }

    for (int i = l; i < r; i += 2) {
        if (s[i] == '.') {
            cout << "NO" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;
}