#include <cstdio>
#define MAXN 5000000
int poz[MAXN+1],v[MAXN+1];
int main(){
    FILE*fi,*fout;
    int i,n,k,b,e;
    long long s;
    fi=fopen("deque.in" ,"r");
    fout=fopen("deque.out" ,"w");
    fscanf(fi,"%d%d" ,&n,&k);
    for(i=1;i<=n;i++)
      fscanf(fi,"%d" ,&v[i]);
    b=0;
    e=-1;
    for(i=1;i<=k;i++){
       while(e>=b&&v[poz[e]]>=v[i])
          e--;
       poz[++e]=i;
    }
    s=v[poz[b]];
    for(i=k+1;i<=n;i++){
        if(i-k>=poz[b])
          b++;
        while(e>=b&&v[poz[e]]>=v[i])
          e--;
        poz[++e]=i;
        s=s+v[poz[b]];
    }
    fprintf(fout,"%lld" ,s);
    fclose(fi);
    fclose(fout);
    return 0;
}