def examine(x, y, arr, n):
for i in vary(1, n):
if arr[i][0] == y or arr[i][1] == y
or arr[i][0] == x or arr[i][1] == x:
proceed
else:
return True
return False
def findIndex(x, arr, n):
for i in vary(1, n):
if arr[i][0] != x and arr[i][1] != x:
return i
return n
def discover(a, n):
x = a[0][0]
ok = findIndex(x, a, n)
if ok >= n:
return 'YES'
y = a[k][0]
flag = 0
if examine(x, y, a, n):
y = a[k][1]
if examine(x, y, a, n):
x = a[0][1]
ok = findIndex(x, a, n)
if ok >= n:
return 'YES'
y = a[k][0]
if examine(x, y, a, n):
y = a[k][1]
if examine(x, y, a, n):
return 'NO'
return 'YES'
if __name__ == '__main__':
N = 6
M = 5
arr = [[2, 3], [2, 4], [2, 5], [3, 4], [3, 5], [4, 5]]
print(discover(arr, N))
