bool prime(int n){    int i = 7, j, q;    if(n == 1)  return false;    if(n == 2 || n == 5 || n == 3)  return true;    if(n % 2 == 0 || n % 3 == 0 || n % 5 == 0)  return false;    q = (int)sqrt((double)n);    for(; i <= q; ){        for(j = 0; j < 8; ++j){            if(n % i == 0)  return false;            i += p[j];        }        if(n % i == 0)  return false;    }    return true;}