#55631: c++ 簡單解
#include <bits/stdc++.h>
using namespace std;
int main(){
int n;
cin>>n;
vector <int> v(n);
for(int i=0;i<n;i++)cin>>v[i];
int total=0;
for(int i=0;i<n;i++){
if(v[i]==0){
if(i==0){v[i]=v[i+1];total+=v[i+1];}
else if(i==n-1){v[i]=v[i-1];total+=v[i-1];}
else {v[i]=min(v[i+1],v[i-1]);total+=min(v[i+1],v[i-1]);}
}
}
cout<<total<<endl;
return 0;
}