import java.util.*;
public class Demo {

    static final int MAX = 1000001;

    static int numofAP(int a[], int n)
    {

        int minarr = +2147483647;
        int maxarr = -2147483648;

        for (int i = 0; i < n; i++) {
            minarr = Math.min(minarr, a[i]);
            maxarr = Math.max(maxarr, a[i]);
        }

        int dp[] = new int[n];
        int sum[] = new int[MAX];

        int ans = n + 1;
        for (int d = (minarr - maxarr);
             d <= (maxarr - minarr); d++)
        {
            Arrays.fill(sum, 0);
            for (int i = 0; i < n; i++) {
                dp[i] = 1;
                if (a[i] - d >= 1 &&
                        a[i] - d <= 1000000)
                    dp[i] += sum[a[i] - d];

                ans += dp[i] - 1;
                sum[a[i]] += dp[i];
            }
        }

        return ans;
    }

    public static void main(String[] args)
    {
        Scanner scanner = new Scanner(System.in);
        int arr[] = Arrays.stream(scanner.nextLine().split(" ")).mapToInt(Integer::parseInt).toArray();
        int n = arr.length;

        System.out.println(numofAP(arr, n));
    }

}