#include <cstdio>
#include <deque>
using namespace std;

const int NMAX = 5000010;

int N, K, V[NMAX];
long long Ans;
deque<int> D;

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

    scanf("%i %i", &N, &K);
    for(int i = 1; i <= N; ++ i)
    {
        scanf("%i", &V[i]);
        while(!D.empty() && V[ D.back() ] >= V[i]) D.pop_back();
        D.push_back(i);
        while(!D.empty() && D.front() <= i - K) D.pop_front();
        if(i >= K) Ans += V[ D.front() ];
    }

    printf("%lld\n", Ans);
}