#include <iostream>
#include<fstream>
#define nmax 5000001

using namespace std;

int deq[nmax],v[nmax];
int main()
{
    int st=1,dr=0,n,i,k;
    long long s=0;
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    for(i=1;i<=n;i++)
    {
        while(st<=dr&&v[deq[dr]]>=v[i])
            dr--;
        deq[++dr]=i;
        while(deq[st]<=i-k)
            st++;
        if(i>=k)
            s+=v[deq[st]];
     }
     fout<<s;
     return 0;
}