{"raw_statement":[{"iden":"problem statement","content":"You are given an integer $N$. Determine whether there exists a simple connected undirected graph with $N$ vertices numbered $1$ to $N$ that satisfies the following condition, and if it exists, show one such graph.\n\n*   There exists an integer $X$ such that for any vertex $v$, the sum of the numbers of all vertices other than $v$ that can be reached from $v$ by traversing an edge once or twice is $X$."},{"iden":"constraints","content":"*   $2 \\le N \\le 200$\n*   All input values are integers."},{"iden":"input","content":"The input is given from Standard Input in the following format:\n\n$N$"},{"iden":"sample input 1","content":"12"},{"iden":"sample output 1","content":"24\n1 2\n2 3\n3 1\n1 4\n4 5\n5 1\n2 6\n6 8\n8 2\n3 7\n7 9\n9 3\n4 6\n6 10\n10 4\n5 7\n7 11\n11 5\n8 9\n9 12\n12 8\n10 11\n11 12\n12 10"},{"iden":"sample input 2","content":"2"},{"iden":"sample output 2","content":"\\-1\n\nIf there does not exist a graph satisfying the condition, print `-1`."}],"translated_statement":null,"sample_group":[],"show_order":["default"],"formal_statement":null,"simple_statement":null,"has_page_source":true}