#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

ifstream fin("operatii.in");
ofstream fout("operatii.out");

const int N = 1e6 + 3;
int v[N], ind = 1;

int main(){
    int n; 
    fin >> n;
    v[0] = v[n + 1] = -1;
    for(int i = 1; i <= n; i++) {
        int x;
        fin >> x;
        if(x == v[ind - 1]) continue;
        v[ind] = x, ind++;
    }
    int ans = 0;
    for(int i = 1; i <= n; i++)
        if(v[i - 1] < v[i] && v[i] > v[i + 1])
            ans += v[i];
    fout << ans;
    return 0;
}