#include<fstream>
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000001],i,p,u,n,k,d[5000001];
long long sum;
int main(){
    fin>> n >> k;
    for( i = 1; i <= n; i++ ){
        fin >> v[i];
    }
    d[1] = 1;
    p = 1;
    u = 1;
    for( int i = 2; i <= n; i++ ){
        while( p <= u && v[i] < v[ d[u] ] ){
            u--;
        }
        d[++u] = i;
        if( i - d[p] == k ){
            p++;
        }
        if( i >= k ){
            sum += v[ d[p] ];
        }
    }
    if( k == 1 ){
        sum += v[1];
    }
    fout << sum;
    return 0;
}