#include<cstdio>
#include<deque>
#define Nmax 2000000000

using namespace std;

int j,i,x,minim(Nmax),n,k;
long long s;
deque <int> v;

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",&x);
        v.push_back(x);
        if(x<minim) minim=x;
        if(i>k)
        {
            if(v.front()<=minim) {minim=Nmax; for(j=1;j!=k;++j)if(v[j]<minim)minim=v[j];}
            v.pop_front();
        }
        if(i>=k) s+=minim;

    }
    printf("%lld\n",s);
    return 0;
}