#include <fstream>

using namespace std;
long long v[5000005],st[5000005];

ifstream in("deque.in");
ofstream out("deque.out");

int main()
{
    int n,k,left,right,i,sum=0;
    in>>n>>k;
    for(i=1;i<=n;i++)
    {
        in>>v[i];
        if(i==1)
        {
            left=right=1;
            st[1]=1;
        }
        else
        {
            while(v[st[right]]>v[i] && right>0)
                right--;
            right++;
            st[right]=i;
            if(st[left]<=i-k) left++;
        }

        if(i>=k) sum+=v[st[left]];
    }
    out<<sum<<'\n';
    return 0;
}