#include<stdio.h>
int n,v[1000000];
void citire()
{
	for(int i=1;i<=n;++i)
		scanf("%d",&v[i]);
}
int main()
{
	int j,nr=0,p=0;
	freopen("operatii.in","r",stdin);
	freopen("operatii.out","w",stdout);
	scanf("%d",&n);
	citire();
	for(int i=1;i<=n;++i)
	{
		if(v[i]==0)
			p=0;
		if(v[i]>v[p])
		{
			nr=nr-v[p]+v[i];
			p=i;
		}
		
	}
	printf("%d",nr);
	return 0;
}