#include<iostream>
#include<algorithm>
using namespace std;
int n,pos;
int a[1000005];
int dp[1000005];
int main(){
    cin >> n;
    for(int i = 1; i <= n; i++) cin >> a[i];
    for(int i = 1; i <= n; i++){
        dp[i] = min(dp[i-1] + a[i], min(dp[i-2] + a[i-1], dp[i-3] + a[i-2]));
    }
    cout << dp[n];
    return 0;
}