#include <stdio.h>

int main() {
	int n,m,v[1000],i;
	scanf("%d",&n); 
	scanf("%d",&v[0]);
	if (n>=2) {scanf("%d",&m);v[1]=(v[0]>m)?v[0]:m;}
	for (i=2;i<n;i++) {
		scanf("%d",&m);
		v[i]=(v[i-1]>v[i-2]+m)?v[i-1]:v[i-2]+m;
	}
	printf("%d",v[n-1]);
	return 0;
}