Language: C++

#
# 　　  ⋀_⋀　 
#　　  (･ω･)  
# .／ Ｕ ∽ Ｕ＼
#  │＊　合　＊│
#  │＊　格　＊│ 
#  │＊　祈　＊│ 
#  │＊　願　＊│ 
#  │＊　　　＊│ 
#      ￣
#
import sys
sys.setrecursionlimit(10**6)
input=sys.stdin.readline
from math import floor,sqrt,factorial,hypot,log #log2ないｙｐ
from heapq import heappop, heappush, heappushpop
from collections import Counter,defaultdict,deque
from itertools import accumulate,permutations,combinations,product,combinations_with_replacement
from bisect import bisect_left,bisect_right
from copy import deepcopy
from fractions import gcd
from random import randint
def ceil(a,b): return (a+b-1)//b
inf=float('inf')
mod = 10**9+7
def pprint(*A): 
    for a in A:     print(*a,sep='\n')
def INT_(n): return int(n)-1
def MI(): return map(int,input().split())
def MF(): return map(float, input().split())
def MI_(): return map(INT_,input().split())
def LI(): return list(MI())
def LI_(): return [int(x) - 1 for x in input().split()]
def LF(): return list(MF())
def LIN(n:int): return [I() for _ in range(n)]
def LLIN(n: int): return [LI() for _ in range(n)]
def LLIN_(n: int): return [LI_() for _ in range(n)]
def LLI(): return [list(map(int, l.split() )) for l in input()]
def I(): return int(input())
def F(): return float(input())
def ST(): return input().replace('\n', '')
def main():
    N=I()
    if(N&1):
        print((N+1)*(N-1)//2 -(N-1))
        pair = N-2
        for i in range(N):
            for j in range(i+1,N):
                if(i+j != pair):
                    print(i+1,j+1)
    else:
        print(N*(N-2)//2)
        pair = N-1
        for i in range(N):
            for j in range(i+1,N):
                if(i+j != pair):
                    print(i+1,j+1)

if __name__ == '__main__':
    main()

Compiler output:
a.cc:2:3: error: extended character 　 is not valid in an identifier
    2 | # 　　  ⋀_⋀　
      |   ^
a.cc:2:3: error: extended character 　 is not valid in an identifier
a.cc:2:3: error: invalid preprocessing directive #\U00003000\U00003000
    2 | # 　　  ⋀_⋀　
      |   ^~~~
a.cc:2:9: error: extended character ⋀ is not valid in an identifier
    2 | # 　　  ⋀_⋀　
      |         ^
a.cc:2:9: error: extended character ⋀ is not valid in an identifier
a.cc:2:9: error: extended character 　 is not valid in an identifier
a.cc:3:2: error: extended character 　 is not valid in an identifier
    3 | #　　  (･ω･)
      |  ^
a.cc:3:2: error: extended character 　 is not valid in an identifier
a.cc:3:2: error: invalid preprocessing directive #\U00003000\U00003000
    3 | #　　  (･ω･)
      |  ^~~~
a.cc:4:3: error: invalid preprocessing directive #.
    4 | # .／ Ｕ ∽ Ｕ＼
      |   ^
a.cc:4:10: error: extended character ∽ is not valid in an identifier
    4 | # .／ Ｕ ∽ Ｕ＼
      |          ^
a.cc:5:4: error: extended character │ is not valid in an identifier
    5 | #  │＊　合　＊│
      |    ^
a.cc:5:4: error: extended character 　 is not valid in an identifier
a.cc:5:4: error: extended character 　 is not valid in an identifier
a.cc:5:4: error: extended character │ is not valid in an identifier
a.cc:5:4: error: invalid preprocessing directive #\U00002502\U0000ff0a\U00003000\U00005408\U00003000\U0000ff0a\U00002502
    5 | #  │＊　合　＊│
      |    ^~~~~~~~~~~~
a.cc:6:4: error: extended character │ is not valid in an identifier
    6 | #  │＊　格　＊│
      |    ^
a.cc:6:4: error: extended character 　 is not valid in an identifier
a.cc:6:4: error: extended character 　 is not valid in an identifier
a.cc:6:4: error: extended character │ is not valid in an identifier
a.cc:6:4: error: invalid preprocessing directive #\U00002502\U0000ff0a\U00003000\U0000683c\U00003000\U0000ff0a\U00002502
    6 | #  │＊　格　＊│
      |    ^~~~~~~~~~~~
a.cc:7:4: error: extended character │ is not valid in an identifier
    7 | #  │＊　祈　＊│
      |    ^
a.cc:7:4: error: extended character 　 is not valid in an identifier
a.cc:7:4: error: extended character 　 is not valid in an identifier
a.cc:7:4: error: extended character │ is not valid in an identifier
a.cc:7:4: error: invalid preprocessing directive #\U00002502\U0000ff0a\U00003000\U00007948\U00003000\U0000ff0a\U00002502
    7 | #  │＊　祈　＊│
      |    ^~~~~~~~~~~~
a.cc:8:4: error: extended character │ is not valid in an identifier
    8 | #  │＊　願　＊│
      |    ^
a.cc:8:4: error: extended character 　 is not valid in an identifier
a.cc:8:4: error: extended character 　 is not valid in an identifier
a.cc:8:4: error: extended character │ is not valid in an identifier
a.cc:8:4: error: invalid preprocessing directive #\U00002502\U0000ff0a\U00003000\U00009858\U00003000\U0000ff0a\U00002502
    8 | #  │＊　願　＊│
      |    ^~~~~~~~~~~~
a.cc:9:4: error: extended character │ is not valid in an identifier
    9 | #  │＊　　　＊│
      |    ^
a.cc:9:4: error: extended character 　 is not valid in an identifier
a.cc:9:4: error: extended character 　 is not valid in an identifier
a.cc:9:4: error: extended character 　 is not valid in an identifier
a.cc:9:4: error: extended character │ is not valid in an identifier
a.cc:9:4: error: invalid preprocessing directive #\U00002502\U0000ff0a\U00003000\U00003000\U00003000\U0000ff0a\U00002502
    9 | #  │＊　　　＊│
      |    ^~~~~~~~~~~~
a.cc:10:8: error: invalid preprocessing directive #\U0000ffe3
   10 | #      ￣
      |        ^~
a.cc:15:49: error: stray '#' in program
   15 | from math import floor,sqrt,factorial,hypot,log #log2ないｙｐ
      |                                                 ^
a.cc:24:11: warning: multi-character character constant [-Wmultichar]
   24 | inf=float('inf')
      |           ^~~~~
a.cc:41:40: error: empty character constant
   41 | def ST(): return input().replace('\n', '')
      |                                        ^~
a.cc:59:16: warning: multi-character literal with 8 characters exceeds 'int' size of 4 bytes
   59 | if __name__ == '__main__':
      |                ^~~~~~~~~~
a.cc:12:1: error: 'import' does not name a type
   12 | import sys
      | ^~~~~~
a.cc:12:1: note: C++20 'import' only available with '-fmodules-ts'