#include <bits/stdc++.h>
using namespace std;
 
void executeTime() {
    cerr << "Time Taken: " << (float)clock() / CLOCKS_PER_SEC << " secs";
}
 
int main() {
 
    int n, b; cin >> n >> b;
 
    vector<int> v(n);
    for (auto &x : v) {
        cin >> x;
    }
 
    vector<int> suffix(n, 0);
    suffix[n - 1] = v[n - 1];
 
    for (int j = n - 2; j >= 0; j--) {
        suffix[j] = v[j] + suffix[j + 1];
    }
 
    int ans = suffix[n - b];
 
    int csum = 0;
    for (int i = 0; i < b - 2; i++) {
        csum += v[i];
 
        int op = csum + suffix[n - (b - (i + 1))];
 
        ans = max(ans, op);
    }
 
    csum += v[b - 1];
 
    ans = max(ans, csum);
 
    cout << ans << endl;
 
    executeTime();
    return 0;
}

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