#include <iostream>
using namespace std;
int main ()
{
    int n;
    cin >> n;
    int a,b,s=0;
    cin >> a >> b;
    int c;
    for (int i = 3 ; i <= n; ++i)
    {
        cin >> c;
        if (a<b && b>c)
            s+=b;
        a=b;
        b=c;
    }
    cout << s;
}