#include <cstdio>
#include <cstring>
#include <algorithm>
#include <set>
#include <map>
#include <vector>
#include <iostream>
using namespace std;
void my_ans(){
    long long i,j,n,m,q,aj,t,k,x=-1,y=-1,w,mi,ma,mid, ans = 0;
    cin>>n;
    long long b[n+1];
    b[0] = 0;
    set<pair<long long,long long>> st;
    set<long long> s1;
    vector<long long> vc;
    pair<long long,long long> p;
    for(i=1;i<=n;++i){
        cin>>t;
        if (t==1){
            b[i] = b[i-1] +1;  vc.push_back(i);
            p.first = t; p.second = -i;st.insert(p);
        }else{
            p.first = t-2;p.second = 0;
            auto it = st.upper_bound(p);
            if (it == st.end()){
                st.clear();b[i] = 0;vc.clear();
            }else{
                p=*it;
                if (p.first == t-1){
                    x = -p.second; m= vc.size()-1;
                    while(m>=0 && vc[m] > x){
                        vc.pop_back();--m;
                    }
                    if (vc[m] < x ) x = vc[m];
                    b[i] = b[x-1] +1;
                    st.erase(p);p.first = t;st.insert(p);
                }else{
                    st.clear();b[i] = 0;vc.clear();
                }
            }
        }
        ans = ans + b[i];
    }
    cout<<ans<<endl;
    return;
}
int main() {
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    long long t=1,i,j;
    //scanf("%d",&t);
    //cin>>t;
    while(t>0){
        --t;my_ans();
    }
    return 0;
}
// 64 位输出请用 printf("%lld")