###### tags: `APCS` `c++`
# 題解 zerojudge g595: 1. 修補圍籬 APCS

#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,h[105],ans=0;
	cin>>n;
	h[0]=101;
	h[n+1]=101;

	int i;
	for(i=1;i<=n;i++){
		cin>>h[i];
	}

	for(i=1;i<=n;i++){
		if(h[i]==0){
			ans+=min(h[i-1],h[i+1]);
		}
	}
	cout<<ans<<"\n";
}