#include <iostream>
#include <list>
#include <vector>
#include <string>
#include <stdio.h>
#include <stdint.h>
#include <iomanip>
using namespace std;

using uint = unsigned int;
using ll = long long;

#define CIN( LL , A ) LL A; cin >> A 
#define GETLINE( A ) string A; getline( cin , A ) 
#define FOR_ITR( ARRAY , ITR , END ) for( auto ITR = ARRAY .begin() , END = ARRAY .end() ; ITR != END ; ITR ++ ) 

int main()
{

  GETLINE( S );
  const uint size = S.size();
  const char a = 'a';
  const char z = 'z';
  const string space = " ";
  
  for( ll i = 0 ; i < size ; i++ ){

    const string s = S.substr( i , 1 );
    
    if( i % 2 == 1 ){

      if( s != space ){

	cout << "No" << endl;
	return 0;
	
      }

    } else {

      const char c = s.c_str()[0];

      if( c < a || z < c ){

	cout << "No" << endl;
	return 0;

      }

    }

  }
  
  cout << "Yes" << endl;
  return 0;

}