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

int n;
vector<long long int> arak, mincost;
void szigetek()
{
    for (int i = 2; i<n; i++) {
        mincost[i] = arak[i] + min(mincost[i-1], mincost[i-2]);
    }
}
int main()
{
    cin>>n;
    arak.resize(n);
    mincost.resize(n);
    for (int i=0; i<n; i++) {
        cin>>arak[i];
    }
    mincost[0] = arak[0];
    mincost[1] = arak[1] + mincost[0];
    szigetek();
    cout << mincost[n-1];
    return 0;
}