public static long repeatedString(string s, long n)
    {
        int countInSingleString = s.Count(c=>c == 'a');
        var quotient = n/s.Length;
        var remainder = n%s.Length;
        var aCnt = countInSingleString * quotient;
        if(remainder > 0)
            aCnt += s.Substring(0,(int)remainder).Count(c=>c =='a');
        return aCnt;
    }