#include <bits/stdc++.h>
#define NMAX 5000000
using namespace std;
deque <int> dq;
long long v[NMAX + 5];
int main()
{
    ifstream fin( "deque.in" );
    ofstream fout( "deque.out" );
    int n, k, i;
    long long sum;
    fin >> n >> k;
    for( i = 1; i <= n; i++ )
      fin >> v[i];
    sum = 0;
    for( i = 1; i <= n; i++ ){
      while( !dq.empty() && v[i] < v[dq.back()] )
        dq.pop_back();
      if( !dq.empty() && dq.front() <= i - k )
        dq.pop_front();
      dq.push_back(i);
      if( i >= k )
        sum += v[dq.front()];
    }
    fout << sum << '\n';
    return 0;
}