// change stack size, in bytes
#pragma comment(linker, "/STACK:33777216") // no spaces !

// regex
regex reg(R"[a-z]+");
string str("couCOU");
bool match = regex_match(str, reg);

// builtins
__gcd(x, y);
// for __builtin_*, add suffix l for long, ll for long long
__builtin_ffs(int);// 1 + least significant 1-bit
// __builtin_ffs(1010b) = 2
// __builtin_ffs(0) = -1
__builtin_clz(unsigned int) // number of leading 0-bits
// __builtin_clz(0..010100b) = 27
// __builtin_clz(0) is undefined
__builtin_ctz(unsigned int) // number of trailing 0-bits
// __builtin_ctz(0..010100b) = 2
// __builtin_ctz(0) is undefined
__builtin_popcount(int) // number of 1-bits
// __builtin_popcount(0110b) = 2

// desynchronise standard i/o
ios::sync_with_stdio(false);