Implements ACL's Math library
Implements atcoder::crt(remainders, modulos).
Implements atcoder::floor_sum(n, m, a, b).
Implements atcoder::inv_mod(value, modulo).
Caluculates a * b % mod without overflow detection
Simplified AtCoder::Math.pow_mod with support of Int64
Returns a * b > target, without concern of overflows.
a * b > target