#include <cstdio>
#include <algorithm>
using namespace std;

int i, N, ANS;
int x, y, Vm;

int main() {
	freopen("operatii.in","r",stdin);
	freopen("operatii.out","w",stdout);
	scanf("%i", &N);
	for (i = 1; i <= N; ++i) {
		scanf("%i", &x);
		if (x == 0) {
			ANS += Vm;
			Vm = 0;
		}
		else
			Vm = max(Vm, x);
	}
	if (x != 0) ANS += Vm;
	printf("%i\n", ANS);
	return 0;
}