#include<stdio.h>
#define Nmax 5000001
using namespace std;
int N,K,v[2][Nmax];
int main()
{
    FILE*f = fopen("deque.in","r");
    fscanf(f,"%d %d",&N,&K);
    int i=1,pos = 0,x,st=1;
    long long sum=0;
    for(i=1;i<=N;++i)
    {
        fscanf(f,"%d ",&x);
        while(pos>=st && v[0][pos] >= x)
            --pos;
        ++pos;
        v[0][pos]       = x;
        v[1][pos]       = i;

        if(i-K == v[1][st])
            ++st;

        if(i>=K)
            sum += v[0][st];
    }
    fclose(f);
    FILE*g = fopen("deque.out","w");
    fprintf(g,"%lld\n",sum);
    fclose(g);
    return 0;
}