#include<cstdio>
#include<queue>
using namespace std;
const int NMAX =5000000;
int v[NMAX+5];
typedef pair <int,int> ii;
deque <ii> q;
int main(){
    int n,i,k;
    long long s=0;
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&v[i]);
    }
    for(i=1;i<=n;i++)
    {
        while(!q.empty()&&q.back().first>=v[i])
            q.pop_back();
        q.push_back(ii(v[i],i));
        if(i>=k)
        {
            while(!q.empty()&&i-q.front().second+1>k)
                q.pop_front();
            s+=q.front().first;
        }
    }
    printf("%lld",s);
}