3.sieve

 #include <bits/stdc++.h>

#include <ext/pb_ds/assoc_container.hpp>

#include <ext/pb_ds/tree_policy.hpp>

using namespace std;

using namespace __gnu_pbds;

template <class type1>

#define ll long long int

#define endl "\n"

#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>

using ordered_multiset = tree <type1, null_type, less_equal <type1>, rb_tree_tag, tree_order_statistics_node_update>;

 //ordered_multiset <ll> kek;(declaration for multiorder set)

// ordered_set o_set;(declaration)

//kek.order_of_key(i);(strictly less then i for multi order set)

//o_set.order_of_key(5) ;(strictly less then i for multi order set)

#define yes cout << "YES\n"

#define no cout << "NO\n"

#define N 100

vector<ll>prime(N);

void sieve()

{

    ll i,j;

    prime[0]=1;

    prime[1]=1;

    for(i=2;i<=N;i++)

    {

         if(prime[i]==0)

         {

            for(j=i*i;j<=N;j+=i)

            {

                prime[j]=1;

            }

         }

    }

}

int main()

{

    ios_base::sync_with_stdio(0);

    cin.tie(0);

    cout.tie(0);

   

   sieve();

   for(ll i=1;i<=10;i++)

   {

      if(prime[i]==0)cout<<i<<" ";

   }

    return 0;

}