Gem Stones

John has discovered various rocks. Each rock is composed of various elements, and each element is represented by a lowercase latin letter from 'a' to 'z'. An element can be present multiple times in a rock. An element is called a 'gem-element' if it occurs at least once in each of the rocks.

Given the list of N rocks with their compositions, display the number of gem-elements that exist in those rocks.

Input Format
The first line consists of N, the number of rocks.
Each of the next N lines contain rocks' composition. Each composition consists of lowercase letters of English alphabet.

Output Format
Print the number of gem-elements that are common in these rocks. If there are none, print 0.

Constraints
1 ≤ N ≤ 100
Each composition consists of only small latin letters ('a'-'z').
1 ≤ Length of each composition ≤ 100

https://www.hackerrank.com/challenges/gem-stones