#include <cstdio>
using namespace std;

FILE *f=fopen("deque.in","r");
FILE *g=fopen("deque.out","w");

const int NMAX=5000001;

int N,K,x;
int v[NMAX],DQ[NMAX];

long long solve()
{
    fscanf(f,"%d%d",&N,&K);
    for(int i=1;i<=N;i++)
        fscanf(f,"%d",&v[i]);
    long long S=0;
    int f=1,b=0;
    for(int i=1;i<=N;i++)
    {
        //
        while(f<=b&&v[i]<=v[DQ[b]])
            b--;
        //
        DQ[++b]=i;
        if(DQ[f]==i-K)
            f++;
        if(i>=K)
            S+=v[DQ[f]];
    }
    return S;
}

int main()
{
    fprintf(g,"%lld",solve());
    return 0;
}