int rand_n(int n)
{
assert(n>=0 && n<=RAND_MAX);
int k=rand();
int M=RAND_MAX/n*n;
while (k>=M)
{
k=rand();
}
return k%n;
}
int rand_n(int n)
{
assert(n>=0 && n<=RAND_MAX);
int k=rand();
int M=RAND_MAX/n*n;
while (k>=M)
{
k=rand();
}
return k%n;
}