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

#define rep(i, a, b) for (ll i = a; i < b; i++)
using ll = long long;

int main(){
    char c1, c2;
    cin >> c1 >> c2;
    string ans = "No";
    if(c1 + 1 == c2 || c1 == c2 + 1) ans = "Yes";
    cout << ans << endl;
}