#include <iostream>
#include <fstream>
#define LL long long
using namespace std;

LL N;

int main(){
    ifstream fin("operatii.in");
    ofstream fout("operatii.out");
    fin >> N;

    LL i,x,MAX=0,res=0;
    for (i=1; i<=N; i++){
        fin >> x;
        if (x==0){
            res+=MAX;
            MAX=0;
        }
        else MAX=max(MAX,x);
    }
    res+=MAX;

    fout << res << "\n";
    return 0;
}