#include <cstdio>
using namespace std;
int n,m,i,j,maxim,nr,x;
int main()
{
    freopen("operatii.in","r",stdin);
    freopen("operatii.out","w",stdout);
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&x);
        maxim=0;
        while(x>0)
        {
            if(maxim<x) maxim=x;
            i++;
            if(i==n+1) break;
            scanf("%d",&x);
        }
        nr+=maxim;
    }
    printf("%d\n",nr);
    return 0;
}