#include <stdio.h>
#include <stdlib.h>

int d[5000001], v[5000000], st, dr, k;

void stanga(int i){
    if(i-k==d[st])
        st++;
}

void dreapta(int i){
    while(st<=dr && v[i]<v[d[dr]])
        dr--;
    d[++dr]=i;
}

int main()
{
    int n, i;
    long long sum;
    FILE *fi=fopen("deque.in", "r"), *fo=fopen("deque.out", "w");
    fscanf(fi, "%d%d", &n, &k);
    for(i=0;i<n;i++)
        fscanf(fi, "%d", &v[i]);
    st=0;
    dr=-1;
    for(i=0;i<k;i++)
        dreapta(i);
    sum=v[d[st]];
    for(i=k;i<n;i++){
        stanga(i);
        dreapta(i);
        sum+=v[d[st]];
    }
    fprintf(fo, "%lld", sum);
    return 0;
}