#include <iostream>
#include <vector>
#include <cmath>
#include <fstream>
#include <map>
//#include <bits/stdc++.h>

using namespace std;

int main() {
    ios::sync_with_stdio(false);
    int N;
    cin >> N;

    long long sum = 0;
    int prev = -1;
    int current_minimum = 2e9;
    for(int i = 0; i < N; i++) {
        int x;
        cin >> x;

        if(prev == -1) {
            prev = x;
            current_minimum = prev;
        }
        else {
            if(prev + 1 == x) {
                current_minimum = min(current_minimum, prev);
            }
            else {
                sum += current_minimum;
                current_minimum = x;
            }
            prev = x;
        }
    }
    cout << sum + current_minimum << endl;

    return 0;
}