Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input = sys.stdin.readline
    sys.setrecursionlimit(10000000)
    from collections import Counter, deque
    #from collections import defaultdict
    from itertools import combinations, permutations
    #from itertools import accumulate, product
    from bisect import bisect_left,bisect_right
    from math import floor, ceil
    #from operator import itemgetter

    #mod = 1000000007

    n,m = map(int, input().split())
    x,y = [], []
    for _ in range(m):
        a,b = map(int, input().split())
        if a==1:
            x.append(b)
        if b==n:
            y.append(a)
    for i in x:
        if i in y:
            print('POSSIBLE')
            exit()
    print('IMPOSSIBLE')


if __name__ == '__main__':
    main()

Fixed submission:
def main():
    import sys
    input = sys.stdin.readline
    sys.setrecursionlimit(10000000)
    from collections import Counter, deque
    #from collections import defaultdict
    from itertools import combinations, permutations
    #from itertools import accumulate, product
    from bisect import bisect_left,bisect_right
    from math import floor, ceil
    #from operator import itemgetter

    #mod = 1000000007

    n,m = map(int, input().split())
    x,y = [], []
    for _ in range(m):
        a,b = map(int, input().split())
        if a==1:
            x.append(b)
        if b==n:
            y.append(a)
    if not len(x)+len(y)==len(set(x+y)):
            print('POSSIBLE')
            exit()
    print('IMPOSSIBLE')


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input = sys.stdin.readline
    sys.setrecursionlimit(10000000)
    from collections import Counter, deque
    #from collections import defaultdict
    from itertools import combinations, permutations
    #from itertools import accumulate, product
    from bisect import bisect_left,bisect_right
    from math import floor, ceil
    #from operator import itemgetter

    #mod = 1000000007

    n,m = map(int, input().split())
    g = [[] for _ in range(n)] 
    for _ in range(m):
        a,b = map(int, input().split())
        g[a-1].append(b-1)
        g[b-1].append(a-1)
    for i in g[0]:
        if i in g[-1]:
            print('POSSIBLE')
            exit()
    print('IMPOSSIBLE')


if __name__ == '__main__':
    main()

Fixed submission:
def main():
    import sys
    input = sys.stdin.readline
    sys.setrecursionlimit(10000000)
    from collections import Counter, deque
    #from collections import defaultdict
    from itertools import combinations, permutations
    #from itertools import accumulate, product
    from bisect import bisect_left,bisect_right
    from math import floor, ceil
    #from operator import itemgetter

    #mod = 1000000007

    n,m = map(int, input().split())
    x,y = [], []
    for _ in range(m):
        a,b = map(int, input().split())
        if a==1:
            x.append(b)
        if b==n:
            y.append(a)
    if not len(x)+len(y)==len(set(x+y)):
            print('POSSIBLE')
            exit()
    print('IMPOSSIBLE')


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    #input = sys.stdin.readline
    sys.setrecursionlimit(10000000)
    from collections import Counter, deque
    #from collections import defaultdict
    from itertools import combinations, permutations
    #from itertools import accumulate, product
    from bisect import bisect_left,bisect_right
    from math import floor, ceil
    #from operator import itemgetter

    #mod = 1000000007

    n,m = map(int, input().split())
    g = [[] for _ in range(n)] 
    for _ in range(m):
        a,b = map(int, input().split())
        g[a-1].append(b-1)
        g[b-1].append(a-1)
    for i in g[0]:
        if i in g[-1]:
            print('POSSIBLE')
            exit()
    print('IMPOSSIBLE')


if __name__ == '__main__':
    main()

Fixed submission:
def main():
    import sys
    input = sys.stdin.readline
    sys.setrecursionlimit(10000000)
    from collections import Counter, deque
    #from collections import defaultdict
    from itertools import combinations, permutations
    #from itertools import accumulate, product
    from bisect import bisect_left,bisect_right
    from math import floor, ceil
    #from operator import itemgetter

    #mod = 1000000007

    n,m = map(int, input().split())
    x,y = [], []
    for _ in range(m):
        a,b = map(int, input().split())
        if a==1:
            x.append(b)
        if b==n:
            y.append(a)
    if not len(x)+len(y)==len(set(x+y)):
            print('POSSIBLE')
            exit()
    print('IMPOSSIBLE')


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    #input = sys.stdin.readline
    sys.setrecursionlimit(10000000)
    from collections import Counter, deque
    #from collections import defaultdict
    from itertools import combinations, permutations
    #from itertools import accumulate, product
    from bisect import bisect_left,bisect_right
    from math import floor, ceil
    #from operator import itemgetter

    #mod = 1000000007

    n,m = map(int, input().split())
    g = [[] for _ in range(n)] 
    for _ in range(m):
        a,b = map(int, input().split())
        g[a-1].append(b-1)
        g[b-1].append(a-1)
    for i in g[0]:
        if i in g[-1]:
            print('POSSIBLE')
            exit()
    print('IMPOSSIBLE')


if __name__ == '__main__':
    main()

Fixed submission:
def main():
    import sys
    input = sys.stdin.readline
    sys.setrecursionlimit(10000000)
    from collections import Counter, deque
    #from collections import defaultdict
    from itertools import combinations, permutations
    #from itertools import accumulate, product
    from bisect import bisect_left,bisect_right
    from math import floor, ceil
    #from operator import itemgetter

    #mod = 1000000007

    n,m = map(int, input().split())
    x,y = [], []
    for _ in range(m):
        a,b = map(int, input().split())
        if a==1:
            x.append(b)
        if b==n:
            y.append(a)
    if not len(x)+len(y)==len(set(x+y)):
            print('POSSIBLE')
            exit()
    print('IMPOSSIBLE')


if __name__ == '__main__':
    main()