#include<stdio.h>
#define max(a,b)	(a>b?a:b)
int n;
int a,b,c,x[100010];
long long f[100010][2];
int main()
{
	scanf("%d",&n);
	for(int i=1;i<=n;i++)
	scanf("%d",&x[i]);
	f[1][1]=x[1];f[1][0]=0;
	for(int i=2;i<=n;i++)
	{
		f[i][1]=f[i-1][0]+x[i];
		f[i][0]=max(f[i-1][0],f[i-1][1]);
	}
	printf("%lld",max(f[n][1],f[n][0]));
	return 0;
} 
/**************************************************************
	Problem: 1653
	User: admin
	Language: C
	Result: Accepted
	Time:29 ms
	Memory:3096 kb
****************************************************************/