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

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