def duplicate_removal(arr):
    dictonary={}
    for i in arr:
        if i in dictonary:
            dictonary[i]=dictonary[i]+1
        else:
            dictonary[i]=1
    return dictonary.keys()

arr=[1,2,2,3,4,5,5,6,7]

print(int(len(list(duplicate_removal(arr)))))