Related: 100299K - Digraphs, 290508668

The first case in test 3 was:

676
aa
ab
ac
...

My output was:

`

That is an illegal character, yet the checker give me an accepted???

It's been 10 (11?) years yet I'm the first one who discover this!?

Through my test this gets accepted:

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int T;
    cin >> T;
    while (T--)
        for (int i = 1; i <= 20; i++)
            puts("````````````````````");
    return 0;
}

As a result, the checker forgot to check whether output consists of illegal characters.

MikeMirzayanov fix this please...