#include <cstdio>
#include <algorithm>

using namespace std;

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