#include <bits/stdc++.h>
using namespace std;
#define INF 1<<30
#define endl '\n'
#define maxn 100005
#define tc printf("Case %d: ", cs)
#define tcn printf("Case %d:\n", cs);
#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
typedef long long ll;
const double PI = acos(-1.0);

#define dbg1(x) cerr << #x << " = " << x << endl;
#define dbg2(x, y) cerr << #x << " = " << x << ", " << #y << " = " << y << endl;
#define dbg3(x, y, z) cerr << #x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = " << z << endl;
#define dbg4(w,x, y, z) cerr << #w << " = " << w << ", " <<#x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = " << z << endl;

template < typename F, typename S >
ostream& operator << ( ostream& os, const pair< F, S > & p ) {
	return os << "(" << p.first << ", " << p.second << ")";
}

template < typename T >
ostream &operator << ( ostream & os, const vector< T > &v ) {
	os << "{";
	for (auto it = v.begin(); it != v.end(); ++it) {
		if ( it != v.begin() ) os << ", ";
		os << *it;
	}
	return os << "}";
}

template < typename T >
ostream &operator << ( ostream & os, const set< T > &v ) {
	os << "[";
	for (auto it = v.begin(); it != v.end(); ++it) {
		if ( it != v.begin()) os << ", ";
		os << *it;
	}
	return os << "]";
}

template < typename F, typename S >
ostream &operator << ( ostream & os, const map< F, S > &v ) {
	os << "[";
	for (auto it = v.begin(); it != v.end(); ++it) {
		if ( it != v.begin() ) os << ", ";
		os << it -> first << " = " << it -> second ;
	}
	return os << "]";
}

#define dbg(args...) do {cerr << #args << " : "; faltu(args); } while(0)

clock_t tStart = clock();
#define timeStamp dbg("Execution Time: ", (double)(clock() - tStart)/CLOCKS_PER_SEC)

void faltu () { cerr << endl; }

template <typename T>
void faltu( T a[], int n ) {
	for (int i = 0; i < n; ++i) cerr << a[i] << ' ';
	cerr << endl;
}

template <typename T, typename ... hello>
void faltu( T arg, const hello &... rest) { cerr << arg << ' '; faltu(rest...); }
// Program showing a policy-based data structure.
#include <ext/pb_ds/assoc_container.hpp> // Common file 
#include <ext/pb_ds/tree_policy.hpp>
#include <functional> // for less 
#include <iostream>
using namespace __gnu_pbds;
using namespace std;
// GNU link : https://goo.gl/WVDL6g
typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
        tree_order_statistics_node_update>
        new_data_set;

/**___________________________________________________**/



int main()
{
	FASTIO
	/*
#ifndef ONLINE_JUDGE
	freopen("in.txt", "r", stdin);
	freopen("out.txt", "w", stdout);
	freopen("error.txt", "w", stderr);
#endif
//*/
	int T;
	//scanf("%d", &T);
	T = 1;
	for (int cs = 1; cs <= T; cs++) {
		int n;
		cin >> n;
		vector<int> v(n + 1);
		int ans = 0;
		int mn = 999;
		int l = 0, r = 0;
		for (int i = 1; i <= n; i++) {
			cin >> v[i];
			if (v[i] > 0) {
				mn = min(mn, v[i]);
			}
			if (v[i] > 0 && l == 0) {
				l = i;
			}
			if (v[i] > 0) r = i;
		}
		if (mn == 999) {
			cout << 0 << endl;
			return 0;
		}
		//	dbg(mn);
		bool flag = false;
		while (1) {
			if (flag) break;
			flag = true;
			int cnt = 1;
			int x = 0, y = 0;
			int M = 999;
			//dbg(l, r);
			int ok = 0;
			for (int i = l; i <= r; i++) {
				if (v[i] == 0 && ok == 0) {
					cnt++;
					ok++;
					continue;
				}
				if (v[i] > 0)ok = 0;
				v[i] -= mn;
				//dbg(v[i], i);
				if (v[i] > 0) {
					M = min(M, v[i]);
				}
				if (v[i] > 0 && x == 0) {
					x = i;
				}
				if (v[i] > 0) y = i;
			}
			l = x;
			r = y;
			//dbg(mn, cnt);
			ans += cnt * mn;
			//dbg(ans);
			if (M != 999) {
				mn = M;
				flag = false;
			}
		}
		cout << ans << endl;
	}
	return 0;
}

Measured memory_bytes: 256