PROBLEM_TOTAL, MUSIC_TOTAL = map(int, input().split())
TIMES = list(map(int, input().split()))
TIME_LIMITS = list(map(int, input().split()))

def main():
    TIMES.sort(reverse = True)
    
    ok, ng = -1, MUSIC_TOTAL
    while abs(ok - ng) > 1:
        med = (ok + ng) // 2
        if judge(med):
            ok = med
        else:
            ng = med
    
    print(ok)

def judge(x):
    if x == 0:
        return True
  
    sub_time_limits = TIME_LIMITS[:x]
    sub_time_limits.sort(reverse = True)
        
    music_i = 0
    for time in TIMES:
        time_limit = sub_time_limits[music_i]
        if time <= time_limit:
            music_i += 1
            if music_i >= x:
                 break
        
    return music_i >= x
    
if __name__ == "__main__":
    main()