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

deque < pair <int,int> > c;
long long rez;
int n,k;

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int i,x;
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&x);
        while(!c.empty() && c.back().first>=x) c.pop_back();

        c.push_back( make_pair(x,i) );

        if(c.front().second==i-k) c.pop_front();

        if(i>=k) rez+=c.front().first;
    }
     printf("%lld\n",rez);
    fclose(stdin);
    fclose(stdout);
    return 0;
}