#include <stdio.h>
int v[1000001] ;
int main()
{
    freopen ( "operatii.in" , "r" , stdin ) ;
    freopen ( "operatii.out" , "w" , stdout ) ;
    register int n , s = 0 , i , k = 0 , j , p , q ;
    scanf ( "%d", &n ) ;
    for ( i = 1 ; i <= n ; i++ )
    {
        scanf ( "%d" , &v[i] ) ;
    }
    for ( i = 1 ; i <= n ; i++ )
    {
        if ( v[i] )
        {
            j = i ;
            do
            {
                j++ ;
            } while ( v[j] ) ;
            k = v[i] ;
            for ( p = i + 1 ; p <= j ; p++ )
            {
                if ( v[p] > k )
                k = v[p] ;
            }
            s += k ;
            i = j ;
        }
    }
    printf ( "%d" , s ) ;
    return 0;
}