#include <bits/stdc++.h>
using namespace std;

int main(){
    bool yes = true;
    string s;
    while(cin >> s){
        if(s.size()>1) yes = false;
        if(s[0] < 'a' || s[0] > 'z') yes = false;
    }
    cout << (yes ? "Yes" : "No") << endl;
    return 0;
}