#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,K,V[5000007],D[5000007],fr=1,bk=0;
long long S=0;
int main()
{
    f>>n>>K;
    for(int i=1;i<=n;++i)f>>V[i];
    for(int i=1;i<=n;++i)
    {
        while(bk>=fr&&V[i]<V[D[bk]]) bk--;
        D[++bk]=i;
        if(i-K==D[fr]) fr++;
        if(i>=K) S+=V[D[fr]];
    }
    g<<S<<'\n';
    return 0;
}