#include <bits/stdc++.h>
using namespace std;
#define int long long int
#define double long double
#define print(a) for(auto x : a) cout << x << " "; cout << endl
const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;
inline int power(int a, int b, int mod=M) {
int x = 1;
a %= mod;
while (b) {
if (b & 1) x = (x * a) % mod;
a = (a * a) % mod;
b >>= 1;
}
return x;
}
//_ ***************************** START Below *******************************
vector<int> a;
int consistency(int n){
vector<int> dpA(n);
vector<int> dpB(n);
vector<int> dpX(n);
dpA[0] = max( 0LL, a[0]);
dpB[0] = max( 0LL, a[0]);
dpX[0] = 0;
for(int i=1; i<n; i++){
dpA[i] = a[i] + max( dpB[i-1] , dpX[i-1] );
dpB[i] = a[i] + max( dpA[i-1] , dpX[i-1] );
dpX[i] = max( { dpA[i-1] , dpB[i-1] , dpX[i-1] } );
}
return max( { dpA[n-1], dpB[n-1] , dpX[n-1] } );
}
int practice(int n){
return 0;
}
void solve() {
int n;
cin>> n;
a.resize(n);
for(int i=0; i<n; i++) cin >> a[i];
cout << consistency(n) << endl;
}
int32_t main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
return 0;
}
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