#include<cstdio>

#include<algorithm>

#include<cstring>

#define N 50005

typedef long long ll;

using namespace std;

ll n,c[N],a[N],b[N],sum[N],f[N],L,q[N],l,r;

ll sq(ll x){return x*x;}

double getD(ll j,ll k)

{

    return 1.0*(f[j]+sq(b[j])-f[k]-sq(b[k]))/(*(b[j]-b[k]));

}

int main()

{

    scanf("%lld%lld",&n,&L);

    for (ll i=;i<=n;i++)

    {

        scanf("%lld",&c[i]);

        sum[i]=sum[i-]+c[i];

        a[i]=sum[i]+i--L;

        b[i]=sum[i]+i;

    }

    for (ll i=;i<=n;i++)

    {

        while (l<r && getD(q[l],q[l+])<(double)a[i]) l++;

        ll t=q[l];

        f[i]=f[t]+sq(b[t])-*a[i]*b[t]+sq(a[i]);

        while (l<r && getD(q[r],i)<getD(q[r-],q[r])) r--;

        q[++r]=i;

    }

    printf("%lld\n",f[n]);

    return ;

}