#include <fstream>

using namespace std;

ifstream cin("deque.in") ;
ofstream cout ("deque.out") ;

int d[5000001] , v[5000001] ;

int main()
{
    int n , k ;
    cin >> n >> k ;
    long long sum = 0 ;
    int st = 0 , dr = 0 ;
    for (int i = 0 ; i < n ; i++) {
        cin >> v[i] ;
        if ( st <= dr && d[st] == i - k ) {
            st++ ;
        }
        while ( st <= dr && v[i] <= v[d[dr]]) {
            dr-- ;
        }
        d[++dr] = i ;
        if ( i >= k - 1) {
            sum+= v[d[st]] ;
        }
    }
    cout << sum ;
    return 0;
}