#include <cstdio>
using namespace std;
int n, k, i, p, u, v[5000010], a[5000010];
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", &v[i]);
    p=1;
    u=0;
    for(i=1; i<k; i++)
    {
        while(v[ a[u] ]>v[i] && u>=p)
            u--;
        a[++u]=i;
    }
    for(i=k; i<=n; i++)
    {
        if(a[p]==i-k)
            p++;
        while(v[ a[u] ]>v[i] && u>=p)
            u--;
        a[++u]=i;
        s+=v[ a[p] ];
    }
    printf("%d\n", s);
    return 0;
}