#include<stdio.h>

#define ll long long
#define maxim(a,b) (a>b ? a : b)

int csec,n,v[1000006];
ll sol;

int main ()
{
    int i;
    freopen("operatii.in","r",stdin);
    freopen("operatii.out","w",stdout);
    scanf("%d",&n);
    for(i=1;i<=n;i++)
        scanf("%d",&v[i]);
    for(i=1;i<=n+1;i++)
        if(!v[i])
        {
            sol+=csec;
            csec=0;
        }
        else
            csec=maxim(csec,v[i]);
    printf("%lld\n",sol);
    return 0;
}