gold batch's problem

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
typedef tree<ll,null_type,less_equal<ll>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;
#define suni ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define endl "\n"
#define mn int main()
#define frac() cout.unsetf(ios::floatfield);cout.precision(6);cout.setf(ios::fixed,ios::floatfield);


const int mx=1e6+123;
bool  isprime[mx];
vector<int>prime;
void primegen(int n){
    memset(isprime,1,sizeof(isprime));
    isprime[1]=0;
    for(int i=2;i<=n;i++){
        for(int j=i+i;j<=n;j+=i)
            isprime[j]=0;
    }
    for(int i=3;i<=n;i++){
        if(isprime[i]) prime.push_back(i);
    }
}
 mn
{
    suni;
    primegen(1e6);
    int n;
    while(cin>>n){
        if(n==0) break;
        int p1=-1,p2=-1;
        for(auto u: prime){
         if(u>n) break;
          int tp1=u,tp2=n-u;
          if(tp2>2 && isprime[tp2]==1){
             p1=tp1;
             p2=tp2;
             break;
          }
        }
        cout<<n<<" = "<<p1<<" + "<<p2<<endl;
    }
}