#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int a[N], n, f[N];
int main()
{
cin >> n;
for (int i = 0; i < n; ++i) cin >> a[i];
f[0] = 0;
f[1] = 0;
for (int i = 2; i <= n; i++) {
f[i] = min(f[i - 2] + a[i - 2], f[i - 1] + a[i - 1]);
}
cout << f[n] << endl;
return 0;
}

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