#include <iostream>
#include <algorithm>
#include <vector>
#include <stdio.h>
#include <cmath>

using namespace std;
typedef uint uint32_t;

int main() {
    int N;
    int v[1005] = {0};
    cin >> N;
    for (int i = 0; i < N; i++) {
        cin >> v[i];
    }

    int p=0;
    bool able=true;
    for (int i = 0; i < N; i++) {
        if (v[i] + v[i+2] < v[i+1]) {
            able=true;
            continue;
        }
        if (v[i] + v[i+2] > v[i+1] + v[i+3] && able) {
            able = false;
            p += v[i];
            continue;
        }
        if (v[i] > v[i+1] && able) {
            able = false;
            p += v[i];
            continue;
        }
        able = true;
    }
    cout << p << endl;
}