#include <cstdio>
#define MAXN 1000000
int v[MAXN+1];
int main(){
    FILE*fi,*fout;
    int i,j,n,max;
    long long con;
    fi=fopen("operatii.in" ,"r");
    fout=fopen("operatii.out" ,"w");
    fscanf(fi,"%d" ,&n);
    for(i=0;i<n;i++)
       fscanf(fi,"%d" ,&v[i]);
    con=i=0;
    while(i<n){
        j=i;
        if(v[i]==0)
            i++;
        else{
          max=0;
          while(j<n&&v[j]>0){
             if(v[j]>max)
                max=v[j];
              j++;
          }
          con+=max;
          i=j;
        }
    }
    fprintf(fout,"%lld" ,con);
    fclose(fi);
    fclose(fout);
    return 0;
}