#include <cstdio>
#include <deque>

using namespace std;
deque<int> Q;
int n,i,k,v[5000010];
long long sol;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    for(i=1;i<k;i++)
    {
        scanf("%d",&v[i]);
        while(Q.size()&&v[Q.back()]>=v[i])Q.pop_back();
        Q.push_back(i);
    }
    for(;i<=n;i++)
    {
        scanf("%d",&v[i]);
        while(Q.size()&&v[Q.back()]>=v[i])Q.pop_back();
        Q.push_back(i);
        if(i-Q.front()==k)Q.pop_front();
        sol+=v[Q.front()];
    }
    printf("%lld",sol);
}