Problem: Fox Ciel is going to publish a paper on FOCS (Foxes Operated Computer Systems, pronounce: "Fox"). She heard a rumor: the authors list on the paper is always sorted in the lexicographical order. 

After checking some examples, she found out that sometimes it wasn't true. On some papers authors' names weren't sorted in lexicographical order in normal sense. But it was always true that after some modification of the order of letters in alphabet, the order of authors becomes lexicographical!

She wants to know, if there exists an order of letters in Latin alphabet such that the names on the paper she is submitting are following in the lexicographical order. If so, you should find out any such order.

Lexicographical order is defined in following way. When we compare s and t, first we find the leftmost position with differing characters: si ≠ ti. If there is no such position (i. e. s is a prefix of t or vice versa) the shortest string is less. Otherwise, we compare characters si and ti according to their order in alphabet.

Input

The first line contains an integer n (1 ≤ n ≤ 100): number of names.

Each of the following n lines contain one string namei (1 ≤ |namei| ≤ 100), the i-th name. Each name contains only lowercase Latin letters. All names are different.

Output

If there exists such order of letters that the given names are sorted lexicographically, output any such order as a permutation of characters 'a'–'z' (i. e. first output the first letter of the modified alphabet, then the second, and so on).

Otherwise output a single word "Impossible" (without quotes).

Examples

Input

3
rivest
shamir
adleman


Output

bcdefghijklmnopqrsatuvwxyz


Input

10
tourist
petr
wjmzbmr
yeputons
vepifanov
scottwu
oooooooooooooooo
subscriber
rowdark
tankengineer


Output

Impossible


Input

10
petr
egor
endagorion
feferivan
ilovetanyaromanova
kostka
dmitriyh
maratsnowbear
bredorjaguarturnik
cgyforever


Output

aghjlnopefikdmbcqrstuvwxyz


Input

7
car
care
careful
carefully
becarefuldontforgetsomething
otherwiseyouwillbehacked
goodluck


Output

acbdefhijklmnogpqrstuvwxyz

Solution (in JAVA):

Solution:
import java.io.Writer;
import java.io.BufferedWriter;
import java.io.OutputStreamWriter;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.IOException;
import java.io.InputStream;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.InputMismatchException;
import java.util.*;
import java.io.*;
import java.math.*;
import java.util.concurrent.TimeUnit;

public class C510{
  static class pair{
    int val, idx;
    pair(int a, int b){
      val=a;
      idx=b;
    }
    public String toString(){
      return "(val: "+val+" idx: "+idx+")";
    }
  }


  static class ProblemSolver{
    static boolean topo(int start, boolean vis[], boolean[] rec){
      if(rec[start])return true;
      if(vis[start]) return false;
      vis[start]=rec[start]=true;
      boolean inside=false;
      for(int i: graph.get(start)){
        if(topo(i, vis, rec)) return true;
      }
      ans.add(start);
      rec[start]=false;
      return false;
    }
    static void bfs(boolean vis[], int start, int []inDegree, int[] outDegree){
      ArrayDeque<Integer> dq= new ArrayDeque<>();
      for(int i=1;i<inDegree.length;i++){
        if(inDegree[i]==0) dq.addFirst(i);
      }
      while(!dq.isEmpty()){
        int temp= dq.removeLast();
        ans.add(temp);
        for(int i: graph.get(temp)){
          inDegree[i]--;
          if(inDegree[i]==0){
            dq.addFirst(i);
          }
        }
      }

    }
    static ArrayList<ArrayList<Integer>> graph=new ArrayList<>();
    static ArrayList<Integer> ans=new ArrayList<>();
    public void solveTheProblem(InputReader in,OutputWriter out, NumberTheory nt, Debug dbg){
      dbg.setLocal(1);
      int test=1;//in.nextInt();
      while(test-- >0){
        // graph.clear();
        // ans.clear();
        int n;
        n=in.nextInt();
        String s[]= new String[n];
        for(int i=0;i<n;i++){
          s[i]=in.nextLine();
        }
        // int inDegree[]= new int[25+1];
        // int outDegree[]= new int[25+1];
        // Arrays.fill(inDegree, -1);
        for(int i=0;i<26;i++) graph.add(new ArrayList<>());
        for(int i=0;i<n;i++){
          char[] temp1= s[i].toCharArray();
          // System.out.printf("inside1 i: %d\t s[i]: %s\t\n", i, s[i]);
          for(int j=i+1;j<n;j++){
            // System.out.println("inside2");
            boolean edgeAdded=false;
            for(int k=0;k<Math.min(s[i].length(), s[j].length());k++){
              if(s[i].charAt(k)!=s[j].charAt(k)){
                // System.out.println("s[i]: "+(s[i].charAt(k)));
                // System.out.println("Edge from: "+(s[i].charAt(k)-'a')+" -->  "+(s[j].charAt(k) -'a'));
                // graph.get(s[i].charAt(k)-'a').add(s[j].charAt(k) -'a');
                // System.out.println("Edge from: "+(s[i].charAt(k))+" -->  "+(s[j].charAt(k)));
                graph.get(s[i].charAt(k)-'a').add(s[j].charAt(k) -'a');
                edgeAdded=true;
                // inDegree[(s[i].charAt(k)-'a')]++;
                // outDegree[(s[j].charAt(k)-'a')]++;
                break;
              }
            }
            if(!edgeAdded){
              if(s[i].length()>s[j].length()){
                out.print("Impossible");
                return;
              }
            }
          }
        }
        // for(int i=0;i<26;i++){
        //   System.out.println((char)(i+'a'));
        // }
        boolean vis[]= new boolean[27];
        boolean rec[]= new boolean[27];
        // System.out.println(graph);
        boolean flag=false;
        // bfs(vis, 0, inDegree, outDegree);
        for(int i=0;i<26;i++){
          if(!vis[i]){
            if(topo(i, vis, rec)){
              flag=true;
              break;
            }
          }
        }
        // System.out.println(flag);
        if(flag) out.print("Impossible");
        else{
          Collections.reverse(ans);
          for(int i: ans){
            out.print((char)(i+'a'));
          }
        }
        // out.println();
        // System.out.println(ans);
        // System.out.println(ans.size());
        // for(int i=0;i<26;i++){
        //   if(graph.get(i).size()==0){
        //     out.print((char)(i+'a'));
        //   }
        // }

      }
    }
  }

  public static void main(String[] args){
    int checkTimeELAPSED=0;
    if(checkTimeELAPSED==0){
      InputStream inputStream=System.in;
      OutputStream outputStream=System.out;
      Debug debug= new Debug();
      InputReader in=new InputReader(inputStream);
      OutputWriter out=new OutputWriter(outputStream);
      NumberTheory nt= new NumberTheory();
      ProblemSolver problemSolver=new ProblemSolver();
      problemSolver.solveTheProblem(in,out, nt, debug);
      out.flush();
      out.close();
    }
    else{
      long startTime = System.nanoTime();
      InputStream inputStream=System.in;
      OutputStream outputStream=System.out;
      Debug debug= new Debug();
      InputReader in=new InputReader(inputStream);
      OutputWriter out=new OutputWriter(outputStream);
      NumberTheory nt= new NumberTheory();
      ProblemSolver problemSolver=new ProblemSolver();
      problemSolver.solveTheProblem(in,out,nt,debug);
      long endTime = System.nanoTime();
      long timeElapsed = endTime - startTime;
      out.println("Execution time in nanoseconds  : " + timeElapsed);
  		out.println("Execution time in milliseconds : "+ timeElapsed / 1000000);
      out.println("Execution time in seconds : "+ timeElapsed / 1000000000);
      out.flush();
      out.close();
    }
  }
  @SuppressWarnings({"unchecked", "static-access", "all", "StaticQualifiedUsingExpression"})
  static class Debug {
	//change to System.getProperty("ONLINE_JUDGE")==null; for CodeForces
    public static boolean LOCAL;
    public void setLocal(int a){
      if(a==1) LOCAL=false;
      else LOCAL=System.getProperty("user.home").toString().equals("C:\\Users\\Hp");
    }
  	private static <T> String ts(T t) {
  		if(t==null) {
  			return "null";
  		}
  		try {
  			return ts((Iterable) t);
  		}catch(ClassCastException e) {
  			if(t instanceof int[]) {
  				String s = Arrays.toString((int[]) t);
  				return "{"+s.substring(1, s.length()-1)+"}";
  			}else if(t instanceof long[]) {
  				String s = Arrays.toString((long[]) t);
  				return "{"+s.substring(1, s.length()-1)+"}";
  			}else if(t instanceof char[]) {
  				String s = Arrays.toString((char[]) t);
  				return "{"+s.substring(1, s.length()-1)+"}";
  			}else if(t instanceof double[]) {
  				String s = Arrays.toString((double[]) t);
  				return "{"+s.substring(1, s.length()-1)+"}";
  			}else if(t instanceof boolean[]) {
  				String s = Arrays.toString((boolean[]) t);
  				return "{"+s.substring(1, s.length()-1)+"}";
  			}
  			try {
  				return ts((Object[]) t);
  			}catch(ClassCastException e1) {
  				return t.toString();
  			}
  		}
  	}
  	private static <T> String ts(T[] arr) {
  		StringBuilder ret = new StringBuilder();
  		ret.append("{");
  		boolean first = true;
  		for(T t: arr) {
  			if(!first) {
  				ret.append(", ");
  			}
  			first = false;
  			ret.append(ts(t));
  		}
  		ret.append("}");
  		return ret.toString();
  	}
  	private static <T> String ts(Iterable<T> iter) {
  		StringBuilder ret = new StringBuilder();
  		ret.append("{");
  		boolean first = true;
  		for(T t: iter) {
  			if(!first) {
  				ret.append(", ");
  			}
  			first = false;
  			ret.append(ts(t));
  		}
  		ret.append("}");
  		return ret.toString();
  	}
  	public void dbg(Object... o) {
  		if(LOCAL) {
  			System.err.print("Line #"+Thread.currentThread().getStackTrace()[2].getLineNumber()+": [");
  			for(int i = 0; i<o.length; i++) {
  				if(i!=0) {
  					System.err.print(", ");
  				}
  				System.err.print(ts(o[i]));
  			}
  			System.err.println("]");
  		}
  	}
  }

  static class InputReader {
    private boolean finished = false;

    private InputStream stream;
    private byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;
    private SpaceCharFilter filter;

    public InputReader(InputStream stream) {
      this.stream = stream;
    }

    public int read() {
      if (numChars == -1) {
        throw new InputMismatchException();
      }
      if (curChar >= numChars) {
        curChar = 0;
        try {
          numChars = stream.read(buf);
        } catch (IOException e) {
          throw new InputMismatchException();
        }
        if (numChars <= 0) {
          return -1;
        }
      }
      return buf[curChar++];
    }

    public int peek() {
      if (numChars == -1) {
        return -1;
      }
      if (curChar >= numChars) {
        curChar = 0;
        try {
          numChars = stream.read(buf);
        } catch (IOException e) {
          return -1;
        }
        if (numChars <= 0) {
          return -1;
        }
      }
      return buf[curChar];
    }

    public int nextInt() {
      int c = read();
      while (isSpaceChar(c)) {
        c = read();
      }
      int sgn = 1;
      if (c == '-') {
        sgn = -1;
        c = read();
      }
      int res = 0;
      do {
        if (c < '0' || c > '9') {
          throw new InputMismatchException();
        }
        res *= 10;
        res += c - '0';
        c = read();
      } while (!isSpaceChar(c));
      return res * sgn;
    }

    public long nextLong() {
      int c = read();
      while (isSpaceChar(c)) {
        c = read();
      }
      int sgn = 1;
      if (c == '-') {
        sgn = -1;
        c = read();
      }
      long res = 0;
      do {
        if (c < '0' || c > '9') {
          throw new InputMismatchException();
        }
        res *= 10;
        res += c - '0';
        c = read();
      } while (!isSpaceChar(c));
      return res * sgn;
    }

    public String nextLine() {
      int c = read();
      while (isSpaceChar(c)) {
        c = read();
      }
      StringBuilder res = new StringBuilder();
      do {
        if (Character.isValidCodePoint(c)) {
          res.appendCodePoint(c);
        }
        c = read();
      } while (!isSpaceChar(c));
      return res.toString();
    }

    public boolean isSpaceChar(int c) {
      if (filter != null) {
        return filter.isSpaceChar(c);
      }
      return isWhitespace(c);
    }

    public static boolean isWhitespace(int c) {
      return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    }

    private String readLine0() {
      StringBuilder buf = new StringBuilder();
      int c = read();
      while (c != '\n' && c != -1) {
        if (c != '\r') {
          buf.appendCodePoint(c);
        }
        c = read();
      }
      return buf.toString();
    }

    public String readLine() {
      String s = readLine0();
      while (s.trim().length() == 0) {
        s = readLine0();
      }
      return s;
    }

    public String readLine(boolean ignoreEmptyLines) {
      if (ignoreEmptyLines) {
        return readLine();
      } else {
        return readLine0();
      }
    }

    public BigInteger readBigInteger() {
      try {
        return new BigInteger(nextLine());
      } catch (NumberFormatException e) {
        throw new InputMismatchException();
      }
    }

    public char nextCharacter() {
      int c = read();
      while (isSpaceChar(c)) {
        c = read();
      }
      return (char) c;
    }

    public double nextDouble() {
      int c = read();
      while (isSpaceChar(c)) {
        c = read();
      }
      int sgn = 1;
      if (c == '-') {
        sgn = -1;
        c = read();
      }
      double res = 0;
      while (!isSpaceChar(c) && c != '.') {
        if (c == 'e' || c == 'E') {
          return res * Math.pow(10, nextInt());
        }
        if (c < '0' || c > '9') {
          throw new InputMismatchException();
        }
        res *= 10;
        res += c - '0';
        c = read();
      }
      if (c == '.') {
        c = read();
        double m = 1;
        while (!isSpaceChar(c)) {
          if (c == 'e' || c == 'E') {
            return res * Math.pow(10, nextInt());
          }
          if (c < '0' || c > '9') {
            throw new InputMismatchException();
          }
          m /= 10;
          res += (c - '0') * m;
          c = read();
        }
      }
      return res * sgn;
    }

    public boolean isExhausted() {
      int value;
      while (isSpaceChar(value = peek()) && value != -1) {
        read();
      }
      return value == -1;
    }

    public String next() {
      return nextLine();
    }

    public SpaceCharFilter getFilter() {
      return filter;
    }

    public void setFilter(SpaceCharFilter filter) {
      this.filter = filter;
    }

    public interface SpaceCharFilter {
      public boolean isSpaceChar(int ch);
    }
    public int[] nextIntArray(int n){
      int[] array=new int[n];
      for(int i=0;i<n;++i)array[i]=nextInt();
      return array;
    }
    public int[] nextSortedIntArray(int n){
      int array[]=nextIntArray(n);
      Arrays.sort(array);
      return array;
    }
    public ArrayList<Integer> nextIntArrayList(int n){
      ArrayList<Integer> ar= new ArrayList<>();
      for(int i=0;i<n;i++)
      ar.add(nextInt());
      return ar;
    }
    public ArrayList<Long> nextLongArrayList(int n){
      ArrayList<Long> ar= new ArrayList<>();
      for(int i=0;i<n;i++)
      ar.add(nextLong());
      return ar;
    }

    public int[] nextSumIntArray(int n){
      int[] array=new int[n];
      array[0]=nextInt();
      for(int i=1;i<n;++i)array[i]=array[i-1]+nextInt();
      return array;
    }
    public long[] nextLongArray(int n){
      long[] array=new long[n];
      for(int i=0;i<n;++i)array[i]=nextLong();
      return array;
    }
    public long[] nextSumLongArray(int n){
      long[] array=new long[n];
      array[0]=nextInt();
      for(int i=1;i<n;++i)array[i]=array[i-1]+nextInt();
      return array;
    }
    public long[] nextSortedLongArray(int n){
      long array[]=nextLongArray(n);
      Arrays.sort(array);
      return array;
    }
    public int[][] nextIntMatrix(int n,int m){
      int[][] matrix=new int[n][m];
      for(int i=0;i<n;++i)
      for(int j=0;j<m;++j)
      matrix[i][j]=nextInt();
      return matrix;
    }

    public int[][] nextIntMatrix(int n){
      return nextIntMatrix(n,n);
    }

    public long[][] nextLongMatrix(int n,int m){
      long[][] matrix=new long[n][m];
      for(int i=0;i<n;++i)
      for(int j=0;j<m;++j)
      matrix[i][j]=nextLong();
      return matrix;
    }

    public long[][] nextLongMatrix(int n){
      return nextLongMatrix(n,n);
    }

    public char[][] nextCharMatrix(int n,int m){
      char[][] matrix=new char[n][m];
      for(int i=0;i<n;++i)
      matrix[i]=next().toCharArray();
      return matrix;
    }

    public char[][] nextCharMatrix(int n){
      return nextCharMatrix(n,n);
    }
  }

  static class OutputWriter {
    private final PrintWriter writer;

    public OutputWriter(OutputStream outputStream) {
      writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
    }

    public OutputWriter(Writer writer) {
      this.writer = new PrintWriter(writer);
    }

    // public void print(char[] array) {
    //     writer.print(array);
    // }

    public void print(Object... objects) {
      for (int i = 0; i < objects.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(objects[i]);
      }
    }

    public void print(int[] array) {
      for (int i = 0; i < array.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(array[i]);
      }
    }

    public void print(double[] array) {
      for (int i = 0; i < array.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(array[i]);
      }
    }

    public void print(long[] array) {
      for (int i = 0; i < array.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(array[i]);
      }
    }

    public void print(char[] array) {
      for (int i = 0; i < array.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(array[i]);
      }
    }

    public void print(String[] array) {
      for (int i = 0; i < array.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(array[i]);
      }
    }

    public void print(int[][] matrix){
      for(int i=0;i<matrix.length;++i){
        println(matrix[i]);
      }
    }

    public void print(double[][] matrix){
      for(int i=0;i<matrix.length;++i){
        println(matrix[i]);
      }
    }

    public void print(long[][] matrix){
      for(int i=0;i<matrix.length;++i){
        println(matrix[i]);
      }
    }

    public void print(char[][] matrix){
      for(int i=0;i<matrix.length;++i){
        println(matrix[i]);
      }
    }

    public void print(String[][] matrix){
      for(int i=0;i<matrix.length;++i){
        println(matrix[i]);
      }
    }

    public void println(int[] array) {
      print(array);
      writer.println();
    }

    public void println(double[] array) {
      print(array);
      writer.println();
    }

    public void println(long[] array) {
      print(array);
      writer.println();
    }

    // public void println(char[] array) {
    //     print(array);
    //     writer.println();
    // }

    public void println(String[] array) {
      print(array);
      writer.println();
    }

    public void println() {
      writer.println();
    }

    public void println(Object... objects) {
      print(objects);
      writer.println();
    }

    public void print(char i) {
      writer.print(i);
    }

    public void println(char i) {
      writer.println(i);
    }

    public void println(char[] array) {
      writer.println(array);
    }

    public void printf(String format, Object... objects) {
      writer.printf(format, objects);
    }

    public void close() {
      writer.close();
    }

    public void flush() {
      writer.flush();
    }

    public void print(long i) {
      writer.print(i);
    }

    public void println(long i) {
      writer.println(i);
    }

    public void print(int i) {
      writer.print(i);
    }

    public void println(int i) {
      writer.println(i);
    }

    public void separateLines(int[] array) {
      for (int i : array) {
        println(i);
      }
    }
  }
  static class NumberTheory{

    /**
    * Modular Arithmetic:
    *  1. (a+b)%c=(a%c+b%c)%c
    *  2. (a*b)%c=(a%c*b%c)%c
    *  3. (a-b)%c=(a%c-b%c+c)%c
    *  4. (a/b)%c=(a%c*(b^-1)%c)%c -- (b^-1 is multiplicative modulo inverse)
    */
    //Modular Addition
    public int modularAddition(int a,int b,int MOD){
      return (a%MOD+b%MOD)%MOD;
    }
    public long modularAddition(long a,long b,long MOD){
      return (a%MOD+b%MOD)%MOD;
    }
    //Modular Multiplication
    public int modularMultiplication(int a,int b,int MOD){
      return ((a%MOD)*(b%MOD))%MOD;
    }
    public long modularMultiplication(long a,long b,long MOD){
      return ((a%MOD)*(b%MOD))%MOD;
    }
    //Modular Subtraction
    public int modularSubtraction(int a,int b,int MOD){
      return (a%MOD-b%MOD+MOD)%MOD;
    }
    public long modularSubtraction(long a,long b,long MOD){
      return (a%MOD-b%MOD+MOD)%MOD;
    }

    /**
    * Binary Exponentiation
    */
    public int binaryExponentiation(int x,int n){
      if(n==0)return 1;
      else if(n%2==0)return binaryExponentiation(x*x,n/2);
      else return x*binaryExponentiation(x*x,(n-1)/2);
    }
    public long binaryExponentiation(long x,long n){
      long result=1;
      while(n>0){
        if(n%2==1)result*=x;
        x=x*x;
        n/=2;
      }
      return result;
    }

    /**
    * Modular Exponentiation
    */
    public int modularExponentiation(int x,int n,int MOD){
      if(n==0)return 1%MOD;
      else if(n%2==0)return modularExponentiation(modularMultiplication(x,x,MOD),n/2,MOD);
      else return modularMultiplication(x,modularExponentiation(modularMultiplication(x,x,MOD),(n-1)/2,MOD),MOD);
    }
    public long modularExponentiation(long x,long n,long MOD){
      long result=1;
      while(n>0){
        if(n%2==1)result=modularMultiplication(result,x,MOD);
        x=modularMultiplication(x,x,MOD);
        n/=2;
      }
      return result;
    }

    /**
    * Factorial of a number
    */
    public long factorials(long n){
      if(n==0)return 1;
      return n*factorials(n-1);
    }

    /**
    * Prime factors of a number
    */
    public ArrayList<Integer> distinctPrimeFactors(int n){
      ArrayList<Integer> factorials=new ArrayList<>();
      int limit=(int)Math.sqrt(n);
      if(n%2==0){
        factorials.add(2);
        while(n%2==0)n/=2;
      }
      for(int i=3;i<=limit;i+=2){
        if(n%i==0){
          factorials.add(i);
          while(n%i==0)n/=i;
        }
      }
      if(n>2)factorials.add(n);
      return factorials;
    }

    public ArrayList<Long> distinctPrimeFactors(long n){
      ArrayList<Long> factorials=new ArrayList<>();
      long limit=(long)Math.sqrt(n);
      if(n%2==0){
        factorials.add((long)2);
        while(n%2==0)n/=2;
      }
      for(long i=3;i<=limit;i+=2){
        if(n%i==0){
          factorials.add(i);
          while(n%i==0)n/=i;
        }
      }
      if(n>2)factorials.add(n);
      return factorials;
    }

    public ArrayList<Integer> primeFactors(int n){
      ArrayList<Integer> factorials=new ArrayList<>();
      int limit=(int)Math.sqrt(n);
      if(n%2==0){
        factorials.add(2);
        while(n%2==0)n/=2;
      }
      for(int i=3;i<=limit;i+=2){
        if(n%i==0){
          factorials.add(i);
          while(n%i==0)n/=i;
        }
      }
      if(n>2)factorials.add(n);
      return factorials;
    }

    public ArrayList<Long> primeFactors(long n){
      ArrayList<Long> factorials=new ArrayList<>();
      long limit=(long)Math.sqrt(n);
      if(n%2==0){
        factorials.add((long)2);
        while(n%2==0)n/=2;
      }
      for(long i=3;i<=limit;i+=2){
        if(n%i==0){
          factorials.add(i);
          while(n%i==0)n/=i;
        }
      }
      if(n>2)factorials.add(n);
      return factorials;
    }

    /**
    * Combination: nCr
    */
    //Naive version
    //(n,r)=(n-1,r-1)+(n-1,r) for r!=0 or r!=n
    //(n,0)=(n,n)=1
    public int binomialCoefficientRecursive(int n,int k){
      if(k==0 || k==n)return 1;//base case
      return binomialCoefficientRecursive(n-1,k-1)+binomialCoefficientRecursive(n-1,k);//recursion
    }

    //Dynamic Programming version(Uses bottom up approach to fill the table)
    //Time complexity: O(n*k)
    //Space complexity: O(n*k)
    public long binomialCoefficientIterative(int n,int k){
      long[][] C=new long[n+1][k+1];
      for(int i=0;i<=n;++i){
        for(int j=0;j<=Math.min(n,k);++j){
          if(j==0 || j==i)C[i][j]=1;
          else C[i][j]=C[i-1][j-1]+C[i-1][j];
        }
      }
      return C[n][k];
    }

    //Pascal's Triangle version(Space efficient program)
    //Time complexity: O(n*k)
    //Space complexity: O(k)
    public long nCr(int n,int r){
      int[] C=new int[r+1];
      C[0]=1;//nC0=1
      for(int i=1;i<=n;++i)
      for(int j=Math.min(i,r);j>0;--j)
      C[j]=C[j]+C[j-1];
      return C[r];
    }

    /**
    * Catlan number:
    *  - Time complexity: O(n*n)
    *  - Auxiliary space: O(n)
    *
    *  NOTE: Time complexity could be reduced to O(n) but it is
    *        possible if and only if n is small or else there is
    *        a chance of getting an overflow. To decrease the time
    *        complexity to O(n) just remember nCr=nCn-r
    */
    public long catlanNumber(int n){
      long[] catlan=new long[n+1];
      catlan[0]=catlan[1]=1;
      for(int i=2;i<=n;++i)
      for(int j=0;j<i;++j)
      catlan[i]+=catlan[j]*catlan[i-1-j];

      return catlan[n];
    }

    /**
    * Greatest Common Divisor(GCD)
    *  - It is also known as Highest Common Factor(HCF)
    *  - Time complexity: log(min(a,b))
    *  - Auxiliary Space: O(1)
    */
    public int gcd(int a,int b){
      if(b==0)return a;
      return gcd(b,a %b);
    }

    public long gcd(long a,long b){
      if(b==0)return a;
      return gcd(b,a%b);
    }

    /**
    * Extended Euclid's Algorithm:
    *  - ax+by=gcd(a,b)
    *  - Time complexity:
    *  -
    */


    /**
    * Least Common Multiple(LCM):
    *  - Time complexity: log(min(a,b))
    *  - Auxiliary Space: O(1)
    */
    public long lcm(long a,long b){
      return (a*b)/gcd(a,b);
    }

  }
}
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//                                        BITSY  ___  CHUCK