#include <fstream>
using namespace std;
int v[5000001], coada[5000001];
ifstream cin("deque.in");
ofstream cout("deque.out");
int main()
{
    int n, k, i, inc=0, sf=0;
    long long s=0;
    cin>>n>>k;
    for( i = 1; i <= n; i++ )
        cin>>v[i];
    for( i = 1; i <= n; i++ ){
        while( inc <= sf && v[coada[sf]] >= v[i] )
            sf--;
        coada[++sf]=i;
        if( i >= k ){
            while( inc <= sf && coada[inc] < i - k + 1 )
                inc++;
            s+=v[coada[inc]];
        }
    }
    cout<<s;
    return 0;
}