#include <bits/stdc++.h>

using namespace std;
#define ll long long 
ll a[1000005], n, s = 0;
signed main()
{
    cin >> n;
    for (ll i = 1; i <= n; ++i)
    {
        cin >> a[i];
        if (i % 2 != 0) s += a[i];
    }
    cout << s;
}

#include <bits/stdc++.h>
#define ll long long
using namespace std;
ll n,dem=0,a;
int main() {
	cin>>n;
	for(int i=0;i<n;i++)
	{
	    cin>>a;
	    if(i%2==1)
	    {
	        dem+=a;
	    }
	}
	cout<<dem;
    return 0;
}