#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include <iostream>
#include <cstdio>
#include <vector>
#include <string>
#include <array>
#include <queue>
#include <deque>
#include <set>
#include <list>
#include <map>
#include <stack>
#include <utility>
#include <algorithm>
#include <numeric>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cctype>
#include <cstring>
#include <climits>
#include <bitset>
#include <complex>
#include <random>
#include <functional>
#include <sstream>
#include <iomanip>

using namespace std;

#define rep(i, n) for(int i=0; i<(n); i++)
#define FOR(i, m, n) for(int i=(m);i<(n);i++)
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(),(x).end()
#define SORT(x) sort((x).begin(),(x).end())
#define REVE(x) reverse((x).begin(),(x).end())
#define mp make_pair
#define pb push_back
#define dump(x)  cout << #x << " = " << (x) << endl;
#define forauto(i, a) for(auto i:a)cout << i << " "; puts("");

typedef long long LL;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef vector<string> VS;
typedef vector<bool> VB;
typedef vector<vector<int>> VVI;
typedef pair<int, int> PII;
typedef pair<double, double> PDD;
typedef complex<double> CD;

int main() {
	int n; cin >> n;
	VI p(n); rep(i, n)cin >> p[i];

	int ans = INT_MAX;
	rep(i, p[0] + 1) {
		int cnt = 0;
		VI a = p;

		cnt += i; a[0] -= i;
		rep(i, n - 1) {
			cnt += a[i] * 2;
			a[i + 1] = max(0, a[i + 1] - a[i]);
			a[i] = 0;
		}
		cnt += a[n - 1];
		ans = min(ans, cnt);
	}
	cout << ans << endl;
}
