#include<iostream>
#include<cstdio>

using namespace std;

int dq[5000005], v[5000005];
int main()
{
    FILE *fin, *fout;
    fin=fopen("deque.in","r");
    fout=fopen("deque.out","w");

    int n, i, k, prim, ultim;
    long long s=0;
    fscanf(fin, "%d %d", &n, &k);
    for(i=0; i<n; i++)
        fscanf(fin, "%d", &v[i]);
    prim=1;
    ultim=0;
    ultim++;
    dq[ultim]=0;
    for(i=1; i<n; i++)
    {
        while(v[i]<v[dq[ultim]] && prim<=ultim)
            {
                ultim--;
            }
        ultim++;
        dq[ultim]=i;
        if(dq[prim]==i-k)
            prim++;
        if(i>=k-1)
            s+=v[dq[prim]];
    }
    fprintf(fout, "%lld", s);

}