#include <bits/stdc++.h>

using namespace std;
const int N = 5000010;
int n,k,p,a[N];
deque<int> q;
int64_t sol;
char b[100010];
void inc()
{
    p++;
    if(p==100000)
    {
        p=0;
        fread(b,1,100000,stdin);
    }
}
void read(int &x)
{
    while(b[p]!='-'&&!isdigit(b[p]))
        inc();
    int semn=1;
    if(b[p]=='-'){semn=-1;inc();}
    x=0;
    while(isdigit(b[p]))
    {
        x=10*x+b[p]-'0';
        inc();
    }
    x*=semn;
}
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    read(n);
    read(k);
    for(int i=1;i<=n;i++)
        read(a[i]);
    for(int i=1;i<k;i++)
    {
        while(q.size()&&a[i]<=a[q.back()])
            q.pop_back();
        q.push_back(i);
    }
    for(int i=k;i<=n;i++)
    {
        while(q.size()&&a[i]<=a[q.back()])
            q.pop_back();
        q.push_back(i);
        if(i-q.front()==k)
            q.pop_front();
        sol+=a[q.front()];
    }
    printf("%lld",sol);
    return 0;
}