hackerearth stack operations

    #include <bits/stdc++.h>
    #define ll long long
    #define ld long double
    #define pb push_back
    #define p_b pop_back
    #define si stack<int>
    #define sll stack<ll>
    #define sc stack<char>
    #define vi vector<int>
    #define vll vector<ll>
    #define mii map<int, int>
    #define msi map<string, int>
    #define mci map<char, int>
    #define qc queue<char>
    #define qi queue<int>
    #define qll queue<ll>
    using namespace std;

    int main(){
        ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        ll n, k;
        cin >> n >> k;
        sll s, t, buf;
        for(int i = 0; i < n; i++){
            ll x;
            cin >> x;
            buf.push(x);
        }

        while(buf.size() > 0){
            s.push(buf.top());
            buf.pop();
        }

        t.push(0);
        if(k > n && n > 1){
            while(s.size() > 0){
                if(t.top() <= s.top()){
                    t.push(s.top());
                    s.pop();
                } else{
                    s.pop();
                }
                k--;
            }

            s.push(t.top());
            k--;

            if(k%2 == 0){
                cout << s.top() << "\n";
            } else{
                cout << t.top() << "\n";
            }

        } else if(n == 1){
            if(k%2 == 0){
                cout << s.top() << "\n";
            } else{
                cout << "-1\n";
            }
        } else{
            while(k-- > 1){
                if(t.top() <= s.top()){
                    t.push(s.top());
                    s.pop();
                } else{
                    s.pop();
                }
            }

            s.push(t.top());
            cout << s.top() << "\n";
        }
        return 0;
    }