#include<bits/stdc++.h>
#define M 200004
using namespace std;
int n, a[M], dp[M];
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
cin >> n;
for(int i = 1; i < n; i++)
cin >> a[i];
dp[1] = a[1];
dp[2] = a[1] + a[2];
for(int i = 3; i < n; i++)
dp[i] = min(dp[i - 1], dp[i - 2]) + a[i];
cout << dp[n - 1];
}
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