#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=1, sf=1;
    long long s=0;
    cin>>n>>k;
    for( i = 1; i <= n; i++ )
        cin>>v[i];
    coada[1]=1;
    for( i = 2; i <= k; i++ ){
        while( inc <= sf && v[coada[sf]] > v[i] )
            sf--;
        coada[++sf]=i;
    }
    s+=v[coada[inc]];
    for( i = k + 1; i <= n; i++ ){
        while( inc <= sf && v[coada[sf]] > v[i] )
            sf--;
        coada[++sf]=i;
        while( inc <= sf && coada[inc] < i - k + 1 )
            inc++;
        s+=v[coada[inc]];
    }
    cout<<s;
    return 0;
}