#include<iostream> #include<cstdio> #include<algorithm> using namespace std; int main() { int n,i,a[100],f[100]={0}; cin>>n; for(i=1;i<=n;++i)cin>>a[i]; f[1]=a[1]; for(i=2;i<=n;++i) f[i]=max(f[i-1],f[i-2]+a[i]); cout<<f[n]<<endl; return 0; }