#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long A[5000010],N,K,j,Min,s,i,p,u,d[5000010];
/*int main()
{
    fin>>N>>K;
    for(i=1;i<=N;i++) fin>>A[i];
    for(i=1;i<=N;i++)
    {
        Min=10000001;
        for(j=0;j<K;j++)
            if(Min>A[i+j]) Min=A[i+j];
        s+=Min;;

    }
    fout<<s;
    return 0;
}
*/
int main()
{
    fin>>N>>K;
    for(i=1;i<=N;i++) fin>>A[i];
    p=u=d[1]=1;
    for(i=2;i<=N;i++)
    {
        while(A[i]<A[d[u]]&&p<=u) --u;
        d[++u]=i;
        if(i-d[p]==K) p++;
        if(i>=K) s+=A[d[p]];
    }
    fout<<s;
}