def reverse(s):
    s1 = ''
    ret=1
    if(len(s)%2 == 0 ):
        for x in range(len(s)-2):
            s1+=s[ret]+s[ret-1]
            ret+=2
        return s1
    else:
        for x in range(len(s)-3):
            s1+=s[ret]+s[ret-1]
            ret+=2
        s1 += s[ret-1]
        return s1

ciao = reverse("bello");
print(ciao);