#include <iostream>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int main()
{
    int n, st = 0, dr = -1, k;
    long long sum = 0;
    in >> n >> k;
    long long v[n+3], d[n+3];
    for(int i = 0 ; i < n ; i++){
        in >> 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]];
    }
    out << sum;
    return 0;
}