#include<cstdio>
long n,i,a[1000000],max,rasp;
int main(){
	freopen("operatii.in","r",stdin);
	freopen("operatii.out","w",stdout);
	scanf("%ld",&n);
	for(i=0;i<n;i++)
		scanf("%ld",&a[i]);
	for(i=0;i<n;i++)
		if(a[i]!=0){
			if(a[i-1]==0 || i==0)max=a[i];
			else if(a[i]>max)max=a[i];
		}
		else{
			rasp+=max;
			max=0;
		}
	if(max!=0)rasp+=max;
	printf("%ld\n",rasp);
	fclose(stdin);
	fclose(stdout);
	return 0;
}