Bruffo

import sys

def missingInt(arr):
    m = sys.maxsize
    M = -sys.maxsize

    for el in arr:
        if el > 0 and el < m:
            m = el
        if el > M:
            M = el

    if m != 1:
        return 1

    arr.append(-1)
    M = min(M, len(arr))
    i = 0
    while i <len(arr):
        if arr[i] == i:
            i += 1
            continue
        if arr[i] >= 1 and arr[i] <= M:
            temp = arr[i]
            if arr[temp] == temp:
                arr[i] = -1
            else:
                arr[i] = arr[temp]
                arr[temp] = temp
        else:
            arr[i] = -1
            i += 1

    succ = 1
    for el in arr:
        if el >= 1 and el <= M:
            if el == succ:
                succ += 1
            else:
                return succ
    return succ