#include <bits/stdc++.h>

using namespace std;

const int NMAX = 5e6;

int v[NMAX + 1];

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