# Task
 You are given two string `a` an `s`. Starting with an empty string we can do the following two operations:
```
append the given string a to the end of the current string.
erase one symbol of the current string.```
Your task is to find the least number of operations needed to construct the given string s. Assume that all the letters from `s` appear in `a` at least once.
# Example
 For `a = "aba", s = "abbaab"`, the result should be `6`.
 Coinstruction:
 `"" -> "aba" -> "ab" -> "ababa" -> "abba" -> "abbaaba" -> "abbaab".`
 So, the result is 6.
 For `a = "aba", s = "a"`, the result should be `3`.
 Coinstruction:
 `"" -> "aba" -> "ab" -> "a".`
 So, the result is 3.
 For `a = "aba", s = "abaa"`, the result should be `4`.
 Coinstruction:
 `"" -> "aba" -> "abaaba" -> "abaab" -> "abaa".`
 So, the result is 4.
# Input/Output
 - `[input]` string `a`
  string to be appended. Contains only lowercase English letters. 
  1 <= a.length <= 20
 - `[input]` string `s`
  desired string containing only lowercase English letters.
  1 <= s.length < 1000
 - `[output]` an integer
  minimum number of operations
def string_constructing(a, s):
    i = 0
    for c in s:
        while a[i % len(a)] != c:
            i += 1
        i += 1
    return (i + len(a) - 1) // len(a) * (len(a) + 1) - len(s)
def string_constructing(a, s):
    i = 0
    for c in s:
        while a[i % len(a)] != c:
            i += 1
        i += 1
    return (i + len(a) - 1) // len(a) * (len(a) + 1) - len(s)