Sum of numbers in string, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            // string str = "4";
            // string str = "1abc23";
            // string str = "geeks4geeks";
            string str = "1abc2x30yz67";
            //string str = "123abc";
            SumOfNumns(str);
            
        }
        public static void SumOfNumns(string a){
            bool isPrvDigit = false;
            string prvDigit = "";
            int sum = 0;
            for (int i=0; i< a.Length; i++)
            {
                 if (Char.IsDigit(a[i])) {
                    prvDigit = prvDigit + a[i];
                    isPrvDigit= true;
                 } else {
                     if(isPrvDigit) {
                         sum = sum + int.Parse(prvDigit);
                     }
                     prvDigit = "";
                     isPrvDigit = false;
                 }
            }
             if(isPrvDigit) {
                         sum = sum + int.Parse(prvDigit);
                     }
             Console.WriteLine("Input string : " + a );
            Console.WriteLine("sum of nums : " + sum);
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,33 sec, absolute running time: 0,3 sec, cpu time: 0,28 sec, average memory usage: 16 Mb, average nr of threads: 3, absolute service time: 0,66 sec