task19
def replace_s(s):
    result = []
    for i, char in enumerate(s):
        if char.lower() == 's' and i != 0 and i != len(s) - 1:
            result.append(s[i-1]*2 + s[i+1])
        else:
            result.append(char)
    return result

s = "test_Stringss"
print(replace_s(s))
