from random import randint

def main():

    sr =''
    for i in range(2500):
        sr += str(randint(0,9))
    s = ""
    m = ""
    for i in sr:
        if i in m:
            m += i
            if len(m) > len(s): s = m
            continue
        m = i
    print("m =",s)

if __name__=="__main__":
    main()