#include <iostream>
#include <fstream>
#include <deque>
#define nmax 5000005

using namespace std;

long long sum;

int n, k;
int A[nmax];
deque <int> deq;

int main() {
    
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    
    fin >> n >> k;
    
    for (int i = 1; i <= n; i++)
        fin >> A[i];
    
    for (int i = 1; i <= n; i++) {
        
        while (!deq.empty() && A[i] < A[deq.back()]) deq.pop_back();
        
        deq.push_back(i);
        
        if (!deq.empty() && deq.front() < i - k + 1)
            deq.pop_front();
        
        if (i >= k)
            sum += A[deq.front()];
        
    }
    
    fout << sum << "\n";
    
    fin.close();
    fout.close();
    
    return 0;
}