POI Task Mushrooms [B]

#include <iostream>
#include <algorithm>

using namespace std;

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int n, t;
    cin >> n >> t;
    long long mx = 0, prefixSum = 0;
    int previous = 0;
    for (int i = 1; i <= n; ++i) {
        int current; cin >> current;
        int movesLeft = t-i+2;
        if (movesLeft <= 0) break;
        mx = max(mx, prefixSum + ((movesLeft/2)+1LL)*previous + ((movesLeft+1LL)/2)*current);
        prefixSum += previous;
        previous = current;
    }
    cout << mx << endl;
    return 0;
}