#include <fstream>
const int NMAX=1000005;
const int LOG=21;

using namespace std;

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

int v[NMAX];
int mini[LOG][NMAX];  ///[.....][.....]

/// mini[j][i] = minimul din intervalul i...i+(2^j)-1 = i...i+2^2-1
/// mini[1][i] = min(i..i+1)
/// mini[j][i] = min(mini[j-1][i],mini[j-1][i+2^(j-1)])
/// i<=k1<=k2<=j, min(i...j) = min(min(i..k2),min(k1...j))

int query(int st,int dr)
{
    int j;
    for(j=0;st+(1<<j)-1<dr;j++) {}
    j--;
    return min(mini[j][st],mini[j][dr-((1<<j)-1)]);
}

int main()
{
    int n,k;
    cin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        cin>>v[i];
        mini[0][i]=v[i];
    }
    for(int j=1;(1<<j)<=n;j++)
    {
        for(int i=1;i+(1<<j)-1<=n;i++)
        {
            mini[j][i]=min(mini[j-1][i],mini[j-1][i+(1<<(j-1))]);
        }
    }
    int sum=0;
    for(int i=1;i<=n-k+1;i++)
    {
        int st=i,dr=i+k-1;
        sum+=query(st,dr);
    }
    cout<<sum<<endl;
    return 0;
}