#include <cstdio>
#include <queue>
using namespace std;
deque <int> q = deque <int> ();

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,i,m,mini,poz,a,j;
    long long s=0;
    scanf("%d %d",&n,&m);
    poz=-1;
    for(i=1;i<=n;i++)
    {
        scanf("%d ",&a);
        q.push_back(a);
        if(i>=m)
        {
            if(poz<0)
            {
            mini=32232332;
            for(j=0;j<m;j++) if(mini>=q[j]) {mini=q[j]; poz=j;}
            }
            s=(long long)(s+mini);
            poz--;
            q.pop_front();
        }
    }
    printf("%lld\n", s);
    return 0;
}