#include <bits/stdc++.h>
using namespace std;
int main()
{
int n,lft=0,rit=0,ans=0,i=0,big;
int arr[100001];
cin >> n;
for (int i=0;i<n;i++)
cin >> arr[i];
while(lft<n)
{
big = 0;
while(rit<n&&arr[rit]>arr[rit+1])
{
int mx = max(arr[rit],arr[rit+1]);
big = max(big,mx);
rit++;
}
rit++;
ans+=big;
lft=rit;
}
cout << ans << endl;
}
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