using System;
using System.Text;
public class MainClass {
static String ReplaceCharString(String s, char c1, String s2) {
StringBuilder res = new StringBuilder();
for (int i = 0; i < s.Length; i++)
if (s[i] == c1)
res.Append(s2);
else
res.Append(s[i]);
return res.ToString();
}
}