CF 256C

#include <algorithm>
#include <bitset>
#include <deque>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

#define fst first
#define snd second
#define all(x) (x).begin(), (x).end()
#define clr( a , v ) memset( a , v , sizeof(a) )
#define pb push_back
#define mp make_pair
#define sz size()
#define FORN( i , s , n ) for( int i = s ; i < (int)(n) ; i++ )
#define FOR( i , n ) FORN( i , 0 , n )
#define FORIT(i,x) for( typeof x.begin() i = x.begin() ; i != x.end() ; i++ )
#define trace(x)    cerr << #x << ": " << x << endl;
#define trace2(x, y) cerr << #x << ": " << x << " | " << #y << ": " << y << endl;
#define read ios::sync_with_stdio(false)

using namespace std;

typedef long long int64;
typedef vector <int> vi;
typedef pair <int,int> ii;
typedef vector <string> vs;
typedef vector <ii> vii;

int a[5001];

int f( int L , int R , int h ){
    if( L > R ) return 0;
    int id, min_h = 1e9+1;
    for( int i = L ; i <= R ; i++ ){
        if( a[i] - h < min_h ){
            min_h = a[i] - h, id = i;
        }
    }
    return min( R - L + 1 , min_h + f( L , id-1 , h + min_h ) + f( id+1 , R , h + min_h ) );
}

int main(){
    int n; cin >> n;
    FOR( i , n ) cin >> a[i];
    cout << f( 0 , n-1 , 0 ) << endl;
    return 0;
}