#include <iostream>
using namespace std;
int *dp;
int *used;
int f(int i){
if(i < 2) return 0;
else{
if(used[i] == 0){
dp[i] = dp[i] + max(f(i-2), f(i-3));
used[i] = 1;
}
return dp[i];
}
}
int main() {
int n, i;
cin >> n;
dp = new int [n+1];
used = new int [n+1];
for(i = 1; i<=n; ++i){
cin >> dp[i];
used[i] = 0;
}
f(n);
cout << dp[n];
return 0;
}
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