C++ :

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
	int n,sum=0;
	cin>>n;
	while(n>9)
	{
		// cout<<n%10<<" ";
		sum=sum+n%10;
		n=n/10;
	}
	// cout<<n<<endl;
	sum=sum+n;
	cout<<sum<<endl;
	return 0;
}

Pascal :

var n,a,b,c,d,e:longint;
begin
 readln(n);
 if n<10 then
  begin
   writeln(n);
   exit;
  end;
 if (n>=10) and (n<=99) then
  begin
   a:=n div 10;
   b:=n mod 10;
   writeln(a+b);
   exit;
  end;
 if (n>=100) and (n<=999) then
  begin
   a:=n div 100;
   b:=n div 10 mod 10;
   c:=n mod 10;
   writeln(a+b+c);
   exit;
  end;
 if (n>=1000) and (n<=9999) then
  begin
   a:=n div 1000;
   b:=n div 100 mod 10;
   c:=n div 10 mod 10;
   d:=n mod 10;
   writeln(a+b+c+d);
   exit;
  end;
if (n>=10000) and (n<=99999) then
  begin
   a:=n div 10000;
   b:=n div 1000 mod 10;
   c:=n div 100 mod 10;
   d:=n div 10 mod 10;
   e:=n mod 10;
   writeln(a+b+c+d+e);
   exit;
  end;
end.