import java.util.*;
class Main{
    public static void main (String[] args) {
        int n=4;
        int [] arr={1,3,5,6};
        int i=0;
        int k=2;
        int count=0;
        Arrays.sort(arr);
        for(int j=0;j<n;j++){
            while(arr[j]-arr[i]>k){
                i++;
            }
            count+=j-i;
        }
        System.out.println(count);
    }
}