#include <fstream.h>

int main(){
    ifstream in("operatii.in");
    ofstream out("operatii.out");
    long long int n,sum=0,i;
    long int nr,max;
    in >>n;
    max=0;
    for(i=0;i<n;i++){
                     in >>nr;
                     if(nr>max)
                               max=nr;
                     if(max>0)          
                                        if(nr==0 || i==n-1){
                                                  sum=sum+max;
                                                  max=0;
                                        }
    }
    out <<sum;
    in.close();
    out.close();
    return 0;
}