#include <cstdio>
#define nmax 5000010
using namespace std;

int k,i,Front,Back,n,a[nmax],dq[nmax];
long long s;
int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    scanf("%d%d", &n, &k);
    for(i=1;i<=n;++i)
        scanf("%d", &a[i]);
    Back=0;Front=0;
    for(i=1;i<=n;++i){
        while(Front<=Back&&a[i]<=a[dq[Back]])
            --Back;
        dq[++Back]=i;
        if(dq[Front]==i-k)
            ++Front;
        if(i>=k) s+=a[dq[Front]];
    }
    printf("%lld", s);
    return 0;
}