#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#if __cplusplus >= 201103L
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#endif

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#if __cplusplus >= 201103L
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#endif
using namespace std;
typedef long long int ll;
typedef long double ld;
typedef vector<ll> vi;
typedef vector<string> vs;
typedef pair<ll,ll> P;
typedef vector<P> vp;
#define REP(i,n) for(int i=0;i<n;i++)
#define FOR(i,m,n) for(int i=m;i<n;i++)
#define REPR(i,n) for(int i=n-1;i>=0;i--)
#define FORR(i,n,m) for(int i=n-1;i>=m;i--)
#define all(in) in.begin(),in.end()
#define ALL(in,K) in,in+K
#define INF 1e18
#define MOD 100000007
#define SIZE 10005
#define PI 	3.14159265358979323846

template<typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val){
    std::fill( (T*)array, (T*)(array+N), val );
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    int a[1000];
    REP(i,n){
        cin >> a[i];
    }
    int ans = 0;
    while(1){
        bool finish = true;
        int min_num = SIZE;
        int start = -1;
        REP(i,n){
            //cout << "!!" << min_num << endl;
            if(a[i] && i < n-1){
                //cout << 12345 << endl;
                finish = false;
                if(a[i])min_num = min(a[i],min_num);
                //cout << "[" << min_num << "]" << endl;
                if(start == -1)start = i;
            }else if(start != -1 || i == n-1){
                if(a[i]){
                    if(start==-1)start = i;
                    if(a[i])min_num = min(a[i],min_num);
                    i++;
                }
                //[i]:
                //cout << start+1 << "~" << i << endl;
                FOR(j,start,i)a[j] -= min_num;
                //[i]:
                //REP(i,n)cout << a[i] << " ";
                //[i]:
                //cout << endl;
                if(min_num!=-SIZE && min_num!=SIZE && start!=-1)ans+= min_num;
                //[i]:cout << ans << endl;
                start = -1;
                min_num = SIZE;
            }
            //cout << min_num << endl;
        }
        if(finish){
            cout << ans << endl;
            return 0;
        }
    }
   return 0;
}

Measured memory_bytes: 256