#include<iostream>
#include<cmath>
using namespace std;
struct qk{
	int h1,h2;
}dp[1000001];
int main(){
	int n;
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>dp[i].h1;
		dp[i].h2=0;
	}
	for(int i=0;i<n;i++){
		if(i==0){
			continue;
		}
		dp[i].h1=dp[i-1].h2+dp[i].h1;
		if(i==1){
			dp[i].h2=dp[i-1].h1;
		}
		else{
			dp[i].h2=min(dp[i-2].h1,dp[i-1].h1);
		}
	}
	cout<<dp[n-1].h2;
}