#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <cmath>
#include <cctype>
#include <vector>
#include <string>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <iterator>
#include <functional>
#include <cassert>
#include <algorithm>

typedef long long LL;
typedef long double LD;
using namespace std;

const int MAX = 100005;

int n;
int h[MAX], prev[MAX], next[MAX];

int main()
{
	freopen("d.in", "r", stdin);
	freopen("d.out", "w", stdout);

	scanf("%d", &n);
	for (int i = 1; i <= n; ++i)
		scanf("%d", &h[i]);
	h[0] = h[n + 1] = 0;

	stack <int> s;
	s.push(0);
	for (int i = 1; i <= n; ++i)
	{
		while (!s.empty() && h[i] <= h[s.top()]) s.pop();
		prev[i] = s.empty() ? 0 : s.top();
		s.push(i);
	}

	while (!s.empty()) s.pop();
	s.push(n + 1);
	for (int i = n; i; --i)
	{
		while (!s.empty() && h[i] <= h[s.top()]) s.pop();
		next[i] = s.empty() ? n + 1 : s.top();
		s.push(i);
	}

	LL ans = 0;
	for (int i = 1; i <= n; ++i)
		ans += h[i] - max(h[prev[i]], h[next[i]]);

	printf("%d\n", ans);

	return 0;
}