#include <fstream>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
long long i, n, k, st, dr, s;
int v[5000002], d[5000002];
int main() {
    cin>>n>>k;
    for(i=1;i<=n;i++){
        cin>>v[i];
    }
    st=1;
    for(i=1;i<=n;i++){
        while(st<=dr && v[d[dr]]>v[i]){
            dr--;
        }
        d[++dr]=i;
        if(i-k+1>d[st])
            st++;
        if(i>=k){
            //cout<<d[st]<<" ";
            s+=1ll*v[d[st]];
        }
    }
    cout<<s;

}