Given a string S, the task is to create a string with the first letter of every word in the string.

Example 1:
Input:
S = "geeks for geeks"
Output: gfg
Example 2:
Input:
S = "bad is good"
Output: big
Your Task:
You don't need to read input or print anything. Your task is to complete the function firstAlphabet() which takes string S as input parameter and returns a string that contains the first letter of every word in S.
Expected Time Complexity: O(|S|)
Expected Auxiliary Space: O(|S|)
Constraints:
1 <= |S| <= 10^{5}
S contains lower case English alphabets
Words have a single space between them.

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