public class Solution {
public string ConvertToBase7(int num) {
var prefix = num >= ? "" : "-";
var list = new List<string>();
StringBuilder sb = new StringBuilder();
num = Math.Abs(num);
do
{
var n = num % ;
sb.Append(n.ToString());
num = num / ;
} while (num != );
var result = sb.ToString() + prefix;
var list2 = result.Reverse();
sb.Clear();
foreach (var c in list2)
{
sb.Append(c);
}
return sb.ToString();
}
}