#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define con_input(v) for(auto it=v.begin();it!=v.end();it++){cin>>*it;}
#define con_debug(v) for(auto it=v.begin();it!=v.end();it++){cerr<<*it<<" ";}cerr<<endl;
using namespace std;
using ll = long long;
template <typename T>T digitsum(T n);
template <typename T>T gcd(T u,T v);
template <typename T>bool isPrime(T n);
template <typename T>vector<pair<T, T>> prime_factor(T n);
long long int intpow(long long int,long long int);
template <typename T>T intlog(T);

int main(){
    char s[100];
    int ans=1,a=0;
    while(scanf("%s",&s)!=EOF){
        if(s[1]!='\0'){
            ans=0;
            break;
        }
    }
    cout<<(ans?"Yes":"No")<<endl;
}