module main;

import std;

void main()
{
	auto N = readln.chomp.to!ulong;
	auto M = readln.chomp.to!ulong;
	if (M == 1uL) {
		while (N % 10 == 0)
			N /= 10;
		writeln(N % 10);
		return;
	}
	while (M % 10 == 0) M /= 10;
	auto L = M;
	while (L % 2 == 0) L >>= 1;
	while (L % 5 == 0) L /= 5;
	if (L != 1uL) {
		writeln(-1);
		return;
	}
	BigInt A = N, B = M, Q, R;
	do {
		divMod(A, B, Q, R);
		A = R * 10;
	} while (R != 0);
	writeln(Q.toDecimalString().stripRight("0")[$-1]);
}