#include<bits/stdc++.h>
using namespace std;
const int maxn=1e5+5;
int n,d[maxn],ans;
void solve(int lo,int hi){
	int minv=100010,pos=-1;
	if(hi-lo<=1){
	ans+=max(d[lo],d[hi]);
	return;	
	}
	for(int i=lo;i<=hi;i++){
		if(minv>d[i]){
			minv=d[i];
			pos=i;
		}
	}
	ans+=minv;
	for(int i=lo;i<=hi;i++){
		d[i]-=minv;
	}
	solve(lo,pos-1);
	solve(pos+1,hi);
}
int main(){
	cin>>n;
	for(int i=1;i<=n;i++) cin>>d[i];
	solve(1,n);
	cout<<ans;
	return 0;
}