#include <iostream>
using namespace std;
int main()
{
int i, j, n;
// read n from the user
cin >> n;
// print out all pairs of natural numbers
// a,b <= n, such that a<b
for (i=1; i<n; i++)
for (j=i+1; j<=n; j++)
cout << i << " " << j << endl;
return 0;
}
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