#include<bits/stdc++.h>
#define ll long long int
#define print(a) for (auto x : a) cout << x << " "; cout << endl
#define print_upto(a,n) for(int i=0;i<n;i++) cout<<a[i]<<" "; cout<<endl
#define take(x,n) for(int i=0;i<n;i++) cin>>x[i];
#define watch(x) cout << (#x) << " is " << (x) << "\n"
#define watch2(x,y) cout <<(#x)<<" is "<<(x)<<" and "<<(#y)<<" is "<<(y)<<"\n"
using namespace std;
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
#ifndef ONLINE_JUDGE
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
freopen("error.txt" , "w" , stderr);
#endif
ll n;
cin >> n;
ll a[1000003] = {0};
for (ll i = 0; i < n; i++) {
cin >> a[i];
}
ll dp[1000009] = {0};
dp[0] = a[0];
dp[1] = a[1];
dp[2] = a[2];
for (ll i = 3; i < n; i++) {
ll v = min(dp[i - 2], dp[i - 3]);
dp[i] = a[i] + min(dp[i - 1], v);
}
if (n == 1)
cout << dp[0] << "\n";
else if (n == 2)
cout << min(dp[0], dp[1]) << "\n";
else {
ll v = min(dp[n - 2], dp[n - 3]);
cout << min(dp[n - 1], v) << "\n";
}
return 0;
}
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