#include <fstream>
#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,i,j,a[5000001],sum,minn;
int main()
{f>>n>>k;sum=0;
for(i=1;i<=n;i++)
f>>a[i];minn=INT_MAX;
for(i=1;i<=k;i++)
if(minn>a[i]) minn=a[i];
sum=sum+minn;
for(i=2;i<=n;i++)
{minn=INT_MAX;
if(i+k-1>n) break;
else
    {for(j=i;j<=i+k-1;j++)
    if(a[j]<minn) minn=a[j];

    sum=sum+minn;
    }

}
g<<sum;

    return 0;
}