#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define all(x) (x).begin(),(x).end()
const int mod=1000000007,MAX=1<<17,INF=1<<30;

int main(){

    string S;
    bool ok=true;
    int cnt=0;
    while(cnt<=100){
        cin>>S;
        if(S.size()!=1) ok=false;
        cnt++;
        //cout<<a<<endl;
    }
    
    if(ok) cout<<"Yes"<<endl;
    else cout<<"No"<<endl;
}