#include <iostream>
#include <fstream>
#define m 1000000000
using namespace std;
    ifstream f("deque.in");
    ofstream g("deque.out");
    int v[5000010];
    int n,k;
    long long s=0;
int main()
{
    int best,i,j;
f>>n>>k;
for(i=1;i<=n;i++)
        cin>>v[i];
for(i=1;i<=n-k+1;i++)
{
best=m;
    for(j=0;j<k;j++)
        if (v[i+j]<best)
        best=v[i+j];
        s=s+best;
}
g<<s;
        return 0;
}