I don't know whether it is optimized or not, but probably the easiest one:
public void lcm(int a, int b)
{
if (a > b)
{
min = b;
max = a;
}
else
{
min = a;
max = b;
}
for (i = 1; i < max; i++)
{
if ((min*i)%max == 0)
{
res = min*i;
break;
}
}
Console.Write("{0}", res);
}