#include<bits/stdc++.h>
using namespace std; 

const int N=100005;
int n,r;
int d[N]={0};
int ans=0,n1=1,n2=1;

void js(int x)
{
	if(x==n+1) return;
	if(d[x]==0) 
	{
		js(x+1);
		return;
	}
	for(r=x;r<=n;r++)
	{
		if(d[r]==0) break;
		d[r]-=1;
	}
	ans++;
	js(x);
	return;
}

int main()
{
	freopen("2018road.in","r",stdin);
	freopen("2018road.out","w",stdout);
	cin>>n>>d[1];
	for(int i=2;i<=n;i++) 
	{
		cin>>d[i];
		if(d[i-1]<d[i]) n2=0;
		if(d[i-1]>d[i]) n1=0;
	}
	if(n1==1 || n2==1) cout<<max(d[1],d[n])<<endl;
	else
	{
		js(1);
		cout<<ans<<endl;
	}
	return 0;
}