#include <stdio.h>
#include <deque>
#define NMAX 5000003

using namespace std;

deque<int> dq;
int v[NMAX];

int main(){
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,k;
    long long sum=0;
    scanf("%d %d",&n,&k);
    for(int i=1;i<=n;++i)
        scanf("%d",&v[i]);
    for(int i=1;i<=n;++i){
        while(!dq.empty() && v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(dq.front()==i-k)
            dq.pop_front();
        if(i>=k) sum+=v[dq.front()];
    }
    printf("%lld\n",sum);
    return 0;
}