#include<iostream>
#include<algorithm>
using namespace std;
int n,m,w[200005],q[200005],f[200005];
int main()
{
int i,h=0,t=0,ans=1e9;
scanf("%d%d",&n,&m);
for(i=1;i<=n;i++)scanf("%d",&w[i]);
for(i=1;i<=n;i++){
if(q[h]<i-m)h++;
f[i]=f[q[h]]+w[i];
while(h<=t&&f[q[t]]>=f[i])t--;
q[++t]=i;
}
for(i=n-m+1;i<=n;i++)ans=min(ans,f[i]);
printf("%d\n",ans);
return 0;
}