#include <iostream>

using namespace std;

int dp[100001][2] = {};
int dijak[100001] = {};

int main()
{
    int N;
    cin >> N;
    for(int i = 1; i <= N; i++){
        cin >> dijak[i];
    }

    dp[1][0] = (1 < 29);
    dp[1][1] = dijak[1];
    for(int i = 2; i <= N; i++){
        dp[i][0] = dp[i-1][1];
        dp[i][1] = min(dp[i-1][0], dp[i-1][1]) + dijak[i];
    }
    cout << dp[N][1] << endl;
    return 0;
}