#include <stdio.h>
int main(void)
{
    long long N;
    long long A[200001];

    scanf("%ld", &N);
    for (int i = 0; i < N; ++i)
        scanf("%ld", &A[i]);
    A[N] = 1000000001LL;
    long long tmp = 1, ans = 0;
    for (int i = 1; i <= N; ++i)
    {
        if (A[i] - A[i - 1] == 1)
        {
            tmp++;
        }
        else
        {
            ans += tmp * (tmp - 1) / 2;
            tmp = 1;
        }
    }
    printf("%ld\n", ans);
    return 0;
}