gcd.cpp

// GCD, LCM
// https://youtu.be/8lm8o8L9Bmw?t=2285
// https://youtu.be/XI8exXVxZ-Q?t=3595
// https://youtu.be/F2p_e6iKxnk?t=843
ll gcd(ll a, ll b) { return b?gcd(b,a%b):a;}
ll lcm(ll a, ll b) { return a/gcd(a,b)*b;}