The LL makes the integer literal of type long long.
So 2LL, is a 2 of type long long.
Without the LL, the literal would only be of type int.
This matters when you’re doing stuff like this:
1 << 40
1LL << 40
With just the literal 1, (assuming int to be 32-bits, you shift beyond the size of the integer type -> undefined behavior).
With 1LL, you set the type to long long before hand and now it will properly return 2^40.