#include <iostream>
#include <string>
#define llint long long

using namespace std;

int main(void)
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	string s;
	while(cin >> s){
		if(s.size() != 1){
			cout << "No" << endl;
			return 0;
		}
	}
	cout << "Yes" << endl;
	
	return 0;
}