/**
* Compute least common multiple (lcm) of arguments \a a and \a b, the smallest
* integer value that is a multiple of both \a a and \a b.
* @param a First number.
* @param b second number.
* @return Least common multiple of values \a a and \a b.
*
* @note This function only works for non-negative values of \a a and \a b.
*/
int LeastCommonMultiple(int a, int b)
{
if (a == 0 || b == 0) return 0; // By definition.
if (a == 1 || a == b) return b;
if (b == 1) return a;
return a * b / GreatestCommonDivisor(a, b);
}
/**
* Compute greatest common divisor (gcd) of \a a and \a b.
* @param a First number.
* @param b second number.
* @return Greatest common divisor of \a a and \a b.
*/
int GreatestCommonDivisor(int a, int b)
{
while (b != 0) {
int t = b;
b = a % b;
a = t;
}
return a;
}
int CommonWhatever(int a) {
int b = 1;
for (int i = 1; i <= 4; i++) {
int c = LeastCommonMultiple(i, a);
b = c > b ? c : b;
}
return b;
}