Extract number at end of string in C#

Question

Probably over analysing this a little bit but how would stackoverflow suggest is the best way to return an integer that is contained at the end of a string.

Thus far

Answer 1

Am I allowed to go crazy with this?

using System.Text;
using System.Linq;

static string GetNum(string input)
{
    StringBuilder sb = new StringBuilder();
    for (int i = input.Length - 1; i >= 0; i--)
    {
        if (input[i] < 48 || input[i] > 57)
            break;

        sb.Append(input[i]);
    }

    return String.Concat(sb.ToString().ToCharArray().Reverse());
}