#include <iostream>
#include <cstdio>
#include <algorithm>
#include <deque>

using namespace std;

deque <int> dq;
int n, k, a[5000050], first, last;
long long s;


int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);

    scanf("%d %d", &n, &k);
    for(int i=1; i<=n; i++){
        scanf("%d", &a[i]);
    }
    for(int i=1; i<=n; i++){
        if(!dq.empty())
            while(a[i]<a[dq.back()]){
                dq.pop_back();
                if(dq.empty())
                    break;
            }
        dq.push_back(i);
        first = dq.front();
        last = dq.back();
        if(dq.front() <= i-k)
            dq.pop_front();
        if(i>=k)
            s+= a[dq.front()];
    }
    printf("%lld\n", s);

    return 0;
}