#include <fstream>
#include <queue>

using namespace std;

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

deque <int> dq;

const int nmax=5000000;

int v[nmax+1];

typedef long long int64;

int main(){
    int n,k;
    fin>>n>>k;
    for(int i=1;i<=n;i++){
        fin>>v[i];
    }
    for(int i=1;i<=k-1;i++){
        while(dq.empty()==0&&v[i]<v[dq.back()]){
            dq.pop_back();
        }
        dq.push_back(i);
    }
    int64 sum=0;
    for(int i=k;i<=n;i++){
        while(dq.empty()==0&&v[i]<v[dq.back()]){
            dq.pop_back();
        }
        dq.push_back(i);
        if(dq.front()<=i-k){
            dq.pop_front();
        }
        sum+=v[dq.front()];
    }
    fout<<sum<<"\n";
    return 0;
}