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

deque<pair<int,int> >d;

int n,k;

int main(){
    int x;
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
        scanf("%d %d",&n,&k);

    long long s = 0;
        for(int i=1;i<=k;i++)
        {
            scanf("%d",&x);
            while( d.size() > 0 && d.back().first >= x)d.pop_back();
            d.push_back( make_pair(x,i) );
        }
        s = d.front().first;
        for(int i=k+1;i<=n;i++)
        {
            scanf("%d",&x);
            while( d.size() > 0 && d.back().first >= x)d.pop_back();
            while( d.size() > 0 && d.front().second <= i-k )d.pop_front();
            d.push_back( make_pair(x,i) );
            s += d.front().first;
        }
    printf("%lld\n",s);
    return 0;
}