// C# program to find smallest

// window containing

// all characters of a pattern.

using System;

public class GFG {

    static int no_of_chars = 256;

    // Function to find smallest

    // window containing

    // all characters of 'pat'

    static String findSubString(String str,

                                String pat)

    {

        int len1 = str.Length;

        int len2 = pat.Length;

        // Check if string's length is

        // less than pattern's

        // length. If yes then no such

        // window can exist

        if (len1 < len2) {

            Console.WriteLine("No such window exists");

            return "";

        }

        int[] hash_pat = new int[no_of_chars];

        int[] hash_str = new int[no_of_chars];

        // Store occurrence ofs characters

        // of pattern

        for (int i = 0; i < len2; i++)

            hash_pat[pat[i]]++;

        int start = 0, start_index = -1,

            min_len = int.MaxValue;

        // Start traversing the string

        // Count of characters

        int count = 0;

        for (int j = 0; j < len1; j++) {

            // Count occurrence of characters

            // of string

            hash_str[str[j]]++;

            // If string's char matches

            // with pattern's char

            // then increment count

            if (hash_str[str[j]] <= hash_pat[str[j]])

                count++;

            // if all the characters are matched

            if (count == len2) {

                // Try to minimize the window

                while (hash_str[str[start]]

                           > hash_pat[str[start]]

                       || hash_pat[str[start]] == 0) {

                    if (hash_str[str[start]]

                        > hash_pat[str[start]])

                        hash_str[str[start]]--;

                    start++;

                }

                // update window size

                int len_window = j - start + 1;

                if (min_len > len_window) {

                    min_len = len_window;

                    start_index = start;

                }

            }

        }

        // If no window found

        if (start_index == -1) {

            Console.WriteLine("No such window exists");

            return "";

        }

        // Return substring starting from start_index

        // and length min_len

        return str.Substring(start_index, min_len);

    }

    // Driver Method

    public static void Main(String[] args)

    {

        String str = "timetopractice";

        String pat = "toc";

        Console.WriteLine(findSubString(str, pat));

    }

}