class Solution:
    def countElements(self, arr):
        hm = dict()
        for n in arr:
            if n in hm:
                hm[n] += 1
            else:
                hm[n] = 1
                
        count = 0
          
        for key, value in hm.items():
            if key + 1 in hm:
                count += hm[key]
        
        return count

s = Solution()
print("Expected: 2")
print("Got:", s.countElements([1, 2, 3]))