#include <fstream>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int n,k,dq[5000000],v[5000000],i;
long long sum;
int main()
{int dr=-1,st=0;
    fin>>n>>k;
    for (i=0;i<n;i++){fin>>v[i];
                       if(st<=dr&&dq[st]==i-k){st++;}
                       while(st<=dr&&v[dq[dr]]>=v[i]){dr--;}
                       dq[++dr]=i;
                       if (i>=k-1){sum+= v[dq[st]];}
    }
    fout<<sum;
}