int Combine(int a, int b)
{
var astr = a.ToString();
var bstr = b.ToString();
var result = new StringBuilder(astr.Length + bstr.Length);
for(var i = 0; i < Math.Max(astr.Length, bstr.Length); i++) {
if (astr.Length > i)
result.Append(astr[i]);
if (bstr.Length > i)
result.Append(bstr[i]);
}
return int.Parse(result.ToString());
}