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

deque< pair<int,int> > dq;
int n,k,num;
long long sol;

int main()
{
    int i,j;
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    scanf("%d",&num);
    dq.push_back( make_pair(num,1) );
    for(i=2;i<k;i++)
    {
        scanf("%d",&num);
        while(!dq.empty() && dq.back().first>=num ) dq.pop_back();
        dq.push_back( make_pair(num,i) );
    }
    for(i=k;i<=n;i++)
    {
        scanf("%d",&num);
        if(dq.front().second==i-k) dq.pop_front();
        while(!dq.empty() && dq.back().first>=num) dq.pop_back();
        dq.push_back( make_pair(num,i) );
        sol+=dq.front().first;
    }
    printf("%lld\n",sol);
    fclose(stdin);
    fclose(stdout);
    return 0;
}