A

#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n;
    string s;
    cin>>n>>s;

    int f = 0;

    for(int i=0; i+1<s.size(); i++)
        f |= ((s[i]=='a' && s[i+1]=='b') ||(s[i]=='b' && s[i+1]=='a'));

    if(f)       cout<<"Yes\n";
    else        cout<<"No\n";
}