#include <iostream>
#include<cstdio>
using namespace std;

int vect[5000005];
int vect2[5000005];
int main()
{
    long long i, n, k, sum, x, y;

    FILE *fin, *fout;
    fin=fopen("deque.in","r");
    fout=fopen("deque.out","w");


    fscanf(fin,"%lld %lld", &n, &k);

    sum=0;
    x=0;
    y=0;
    for(i=0; i<n; i++)
    {
        fscanf(fin,"%d",&vect2[i]);
        if(vect[x]==i-k)
            x++;
        while(x<=y && vect2[i]<=vect2[vect[y]])
        {
            y--;
        }
        vect[++y]=i;
        if(i+1>=k)
            sum+= vect2[vect[x]];
    }
    fprintf(fout,"%lld\n", sum);

    return 0;
}