#include<fstream>
using namespace std;
ifstream F("deque.in");
ofstream G("deque.out");
#define N 5000005
int n,k,i,j,q[N],a[N],l,r;
long long s;
int main()
{
    for(F>>n>>k,i=1;i<=n;q[++r]=i,++i) {
        for(F>>a[i];l<=r&&a[q[r]]>=a[i];--r);
        if(i-q[l]==k)
            ++l;
        if(i>=k)
            s+=a[q[l]];
    }
    return G<<s,0;
}