codeforces - even picture

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int , int>
#define fast()(ios_base::sync_with_stdio(0),cin.tie(NULL));
int main()
{
    fast()
    int n;
    cin>>n;
    int x[]={1,-1,0,0};
    int y[]={0,0,1,-1};
    int x_ord=1,y_ord=1;
    set<pii>v;
    v.insert(make_pair(0,0));
    while(n--)
    {
        v.insert(make_pair(x_ord,y_ord));
        for(int i=0;i<4;i++)v.insert(make_pair(x_ord+x[i],y[i]+y_ord));
        x_ord++,y_ord++;
    }
    v.insert(make_pair(x_ord,y_ord));
    cout<<v.size()<<endl;
    for(auto x: v)
    {
        cout<<x.first<<" "<<x.second<<endl;
    }
}