#include <bits/stdc++.h>
#include <vector>
using namespace std;

int main(){
    int length = 1;
    int N;
    int ans = 0;
    scanf("%d",&N);
    int a[N];
    for(int i=0;i<N;i++){
        scanf("%d",&a[i]);
    }
    for(int i=0;i<N-1;i++){
        if(a[i] +1 == a[i+1]){
            length++;
        } else {
            ans += length*(length-1)/2;
            length = 1;
        }
    }
    printf("%d",length);
}