#include template inline bool chmin(T&a, T b){if(a > b){a = b; return true;}else{return false;}} template inline bool chmax(T&a, T b){if(a < b){a = b; return true;}else{return false;}} #define ll long long #define double long double #define rep(i,n) for(int i=0;i<(n);i++) #define REP(i,n) for(int i=1;i<=(n);i++) #define mod (ll)(1e9+7) #define inf (ll)(3e18+7) #define eps (double)(1e-9) #define pi (double) acos(-1) #define P pair #define PiP pair> #define all(x) x.begin(),x.end() #define rall(x) x.rbegin(),x.rend() using namespace std; int main() { int n; cin >> n; vector

ans; REP(i, n){ for(int j = i; j <= n-i; j++)ans.push_back({n-i+1, j}); } cout << ans.size() << endl; for(auto x : ans)cout << x.first << " " << x.second << " " << endl; }