#include <bits/stdc++.h>
#define VuDucNam ios_base::sync_with_stdio(false);
#define Lop9a6 cin.tie(NULL);
#define THCSPhamVanDong cout.tie(NULL);
#define ll long long
#define el cout << '\n'
#define sz(a) (ll) a.size()
#define all(a) a.begin(), a.end()
#define fi first
#define se second
#define fill(a, x) memset(a, x, sizeof(a))
#define file(name)                        \
    if (fopen(name ".inp", "r"))          \
        freopen(name ".inp", "r", stdin); \
        freopen(name ".out", "w", stdout);
#define TIME (1.0 * clock() / CLOCKS_PER_SEC)
#define RUNTIME cerr << "\nRuntime: " << TIME << "s.\n"

using namespace std;

const ll MOD = 1e9 + 7;
const ll inf = LLONG_MAX;

int n,a[25005],dp[25005][6];

void solve()
{
    cin >> n;
    for(int i=1;i<n;++i)
        cin >> a[i];
    dp[1][0]=a[1];
    dp[1][1]=a[1];
    for(int i=2;i<n-1;++i){
        dp[i][0]=dp[i-1][1];
        dp[i][1]=min(dp[i-1][0],dp[i-1][1]) + a[i];
    }
    int ans=min(dp[n-2][0],dp[n-2][1]) + a[n-2];
    cout << ans;
    el;
}

int main()
{
    VuDucNam Lop9a6 THCSPhamVanDong
    // file();
    solve();
    return 0;
}