#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
    int N;
    cin >> N;
    vector<int> V(N);
    for (int i = 0; i < N; i++) {
        cin >> V[i];
    }
    
    int m = 0;
    if (N == 1) {
        m = V[0];
    }
    else {
        int c = 0;
        for (int i = 0; i < N-1; i++) {
            m += max(V[c], V[c+1]);
            if (V[c] > V[c+1]) c += 2;
            else c += 2+1;
        }
    }
    cout << m << endl;
    return 0;
}