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

multiset<int>s;
int v[5000005],n,k;

int main(){
    int sum;
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
        scanf("%d %d",&n,&k);
        for(int i=1;i<=k;i++)
        {
            scanf("%d",&v[i]);
            s.insert(v[i]);
        }
        sum=*s.begin();
        for(int i=k+1;i<=n;i++)
        {
            scanf("%d",&v[i]);
            s.erase(v[i-k]);
            s.insert(v[i]);
            sum+=*s.begin();
        }
        printf("%d\n",sum);
    return 0;
}