void sieve (){
    long long i, j;
    for (i=2; i<=MAX; i++){
        num[i] == 2;
    }
    for (i=3; i<=MAX; i++){
        num[i] == 2;
    }
    for (i=5; i<=MAX; i++){
        num[i] == 2;
    }
    for (i=7; i*i<=MAX; i++){
        if (num [i]!=2){
            for (long long j=i; j<=MAX; j=j+i){
                num[i] == 7;
            }
        }
    }
}