//
// Created by yamunaku on 2020/04/01.
//

#include <bits/stdc++.h>

using namespace std;

#define rep(i, n) for(int i = 0; i < (n); i++)
#define repl(i, l, r) for(int i = (l); i < (r); i++)
#define per(i, n) for(int i = ((n)-1); i >= 0; i--)
#define perl(i, l, r) for(int i = ((r)-1); i >= (l); i--)
#define all(x) (x).begin(),(x).end()
#define MOD9 998244353
#define MOD1 1000000007
#define IINF 1000000000
#define LINF 1000000000000000000
#define SP <<" "<<
#define CYES cout<<"Yes"<<endl
#define CNO cout<<"NO"<<endl
#define CFS cin.tie(0);ios::sync_with_stdio(false)
#define CST(x) cout<<fixed<<setprecision(x)

using ll = long long;
using ld = long double;
using vi = vector<int>;
using mti = vector<vector<int>>;
using vl = vector<ll>;
using mtl = vector<vector<ll>>;
using pi = pair<int, int>;
using pl = pair<ll, ll>;
template<typename T>
using heap = priority_queue<T, vector<T>, function<bool(const T, const T)>>;

int main(){
    //CFS;
    string s;
    getline(cin, s);
    int n = s.size();
    if(n == 1){
        CNO;
        return 0;
    }
    map<int, int> a, b;
    int tt = 0;
    rep(i, n){
        if(s[i] != ' ') tt++;
        if(i & 1){
            if(s[i] != ' '){
                a[s[i] - 'a'] = true;
            }
        }else{
            if(s[i] != ' '){
                b[s[i] - 'a'] = true;
            }
        }
    }
    string t = s;
    int x = tt, y = tt;
    rep(i, n){
        if(a[s[i] - 'a'] && s[i] != ' ') s[i] = ' ', x--;
        if(b[t[i] - 'a'] && t[i] != ' ') t[i] = ' ', y--;
    }
    bool ok1 = true, ok2 = true;
    if(x == 0) ok1 = false;
    if(y == 0) ok2 = false;
    int sta1 = 0, sta2 = 0;
    rep(i, n){
        if(i & 1){
            if(t[i] != ' '){
                if(sta2 == 2){
                    ok2 = false;
                }
                sta2 = 1;
            }else{
                if(sta2 == 0) sta2 = 2;
            }
        }else{
            if(s[i] != ' '){
                if(sta1 == 2){
                    ok1 = false;
                }
                sta1 = 1;
            }else{
                if(sta1 == 0) sta1 = 2;
            }
        }
    }
    if(ok1 || ok2) CYES;
    else
        CNO;
    return 0;
}