#include <bits/stdc++.h>

using namespace std;

int main()
{
    freopen("operatii.in","r",stdin);
    freopen("operatii.out","w",stdout);
    int n,maxx=0,x;
    long long ans=0;
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&x);
        if(x==0) {ans+=maxx;maxx=0;}
        else maxx=max(maxx,x);
    }
    ans+=maxx;
    printf("%lld",ans);
    return 0;
}