#include<fstream>
#include<deque>
using namespace std;
ifstream fi("deque.in");
ofstream fo("deque.out");
int D[5000001];
long long n,i,sum,k,A[5000001],x,y;
int main()
{
    fi>>n>>k;
    for(i=1; i<=n; i++)
        fi>>A[i];
    x=1;
    y=0;
    for(i=1; i<=n; i++)
    {
        while(x<=y && A[i]<=A[D[y]])
            y--;
        D[++y]=i;
        if(D[x]==i-k)
            x++;
        if(i>=k)
            sum+=A[D[x]];
    }
    fo<<sum<<"\n";
    fi.close();
    fo.close();
    return 0;
}