public static void main(String[] args){

Scanner s=new Scanner(System.in);

String str=new String();

str="1,9,3,10,4,20,2";

int[] arr=new int[10];

int j=0;

int k;

for(String i:str.split(",",0)){

k=Integer.parseInt(i);

arr[j]=k;

j++;

}

Arrays.sort(arr);

int n = arr.length;

System.out.println("Length of the Longest consecutive subsequence is " +

findLongestConseqSubseq(arr,n));

}

static int findLongestConseqSubseq(int arr[],int n)

{

HashSet<Integer> S = new HashSet<Integer>();

int ans = 0;

// Hash all the array elements

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

S.add(arr[i]);

// check each possible sequence from the start

// then update optimal length

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

{

// if current element is the starting

// element of a sequence

if (!S.contains(arr[i]-1))

{

// Then check for next elements in the

// sequence

int j = arr[i];

while (S.contains(j))

j++;

// update optimal length if this length

// is more

if (ans<j-arr[i])

ans = j-arr[i];

}

}

return ans;

}

}