#include <fstream>
#define NM 5000003
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long long n,k,i,bk,sum,fr;
int dq[NM],a[NM];
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++) f>>a[i];
    bk=1; fr=0;
    for(i=1;i<=n;i++){
        while(fr<=bk&&a[i]<=a[dq[bk]]) bk--;
        dq[++bk]=i;
        if(dq[fr]==i-k) fr++;
        if(i>=k) sum+=a[dq[fr]];
    }
    g<<sum<<'\n';
    return 0;
}