#include<stdio.h>

int main (void){
	int N,A[1000],ans[1000],i;
	
	scanf("%d",&N);
	
	for(i=0;i<N;i++){
		scanf("%d",&A[i]);
	}
	
	if(N == 1){
		printf("%d",A[0]);
		return 0;
	}
	
	if(N == 2){
		if(A[0]<A[1]){
			printf("%d",A[1]);
			return 0;
		}else{
			printf("%d",A[0]);
			return 0;
		}
			
	}
	
	if(A[0]<A[1]){
		ans[1] = A[1];
	}else{
		ans[1] = A[0];
	}
	
	if(A[1]<A[0]+A[2]){
		ans[2] = A[0]+A[2];
	}else {
		ans[2] = A[1];
	}
	
	if(N == 3){
		printf("%d",ans[2]);
		return 0;
	}
	
	for(i=3;i<=N-1;i++){
		
		if(ans[i-1] < ans[i-2]+A[i]){
			ans[i] = ans[i-2]+A[i];
		}else {
			ans[i] = ans[i-1];
		}
	}
	
	printf("%d",ans[N-1]);
}