#include <iostream>
using namespace std;
int main() {
// your code goes here
int n;
cin>>n;
int a[n+1];
for(int i=1;i<=n;i++)
{
cin>>a[i];
}
int dp[n+1]={0};
dp[1]=max(a[1],0);
dp[2]=max(a[1],max(a[2],0));
int i=3;
while(i<=n)
{
dp[i]=max(a[i]+dp[i-2],dp[i-1]);
i++;
}
cout<<dp[n];
return 0;
}
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