#include<cstdio>
#include<utility>
#include<deque>
using namespace std;
int main()
{
    long long int n,k,x,i,s=0;
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%lld%lld",&n,&k);
    deque<pair<int,int> > D;
    for(i=1;i<=n;i++)
    {
        scanf("%lld",&x);
        while((!D.empty())&&(x<=D.back().first)) D.pop_back();
        D.push_back(make_pair(x,i));
        if(D.front().second==i-k) D.pop_front();
        if(i>=k) s+=D.front().first;
    }
    printf("%lld",s);
    return 0;
}