def truncate_string(str, N):
    substr = str[0: N]
    last_alpha = 0
    for i in range(N - 1, 0, -1):
        if str[i-1].isalpha() and not str[i].isalpha():
            last_alpha = i
            break
    return substr[0: last_alpha] + "…"
    
print(truncate_string("Lorem ipsum dolor sit amet!! Consectetur?! Adipiscing elit... Nam tincidunt ultricies congue (turpis duis).", 40))# your code goes here