#include<iostream>
using namespace std;
int N;
int A[2<<17];
int main()
{
    cin>>N;
    for(int i=0;i<N;i++)cin>>A[i];
    int r=0;
    long ans=0;
    for(int l=0;l<N;l++)
    {
        if(r<=l)r=l+1;
        while(r<N&&A[r]==A[r-1]+1)r++;
        ans+=r-l-1;
    }
    cout<<ans<<endl;
}