int primes[N], cnt, vis[N];

void get_primes(int n){

    for(int i = 2; i <= n;i++){
        if(!vis[i]) primes[cnt++] = i;
            for(int j = 0; primes[j]  <= n/i; j++){
                vis[primes[j]*i] = 1;
                if(i%primes[j] == 0) break;
            }

    }
}