#include <deque>
#include <fstream>

using namespace std;

typedef long long i64;

ifstream fin("deque.in");
ofstream fout("deque.out");

const int nmax= 5000000;

int v[nmax+1];

deque <int> d;

int main(  ) {
    int n, k;
    fin>>n>>k;
    i64 sol= 0;
    for ( int i= 1; i<=n; ++i ) {
        fin>>v[i];
        while ( d.empty()==0 && v[d.back()]>v[i] ) {
            d.pop_back();
        }
        d.push_back(i);
        if ( d.front()<=i-k ) {
            d.pop_front();
        }
        if ( i>=k ) {
            sol+= v[d.front()];
        }
    }
    fout<<sol<<"\n";

    return 0;
}