import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int n = Integer.parseInt(br.readLine());
		String[] sa = br.readLine().split(" ");
		int[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sa[i]);
		}
		br.close();

		long ans = 0;
		int r = 1;
		for (int l = 0; l < n; l++) {
			r = Math.max(r, l + 1);
			while (r < n) {
				if (a[r - 1] + 1 == a[r]) {
					r++;
				} else {
					break;
				}
			}
			ans += r - l - 1;
		}
		System.out.println(ans);
	}
}