#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int v[5000002],d[5000002];


int main(){
    long long n,i,S,pr,ul,k;
    fin>>n;
    fin>>k;
    for(i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    pr=1;ul=1;d[1]=1;
    for(i=2;i<=k;i++)
    {
        while(pr<=ul&&v[d[ul]]>=v[i])
            ul--;
        ul++;
        d[ul]=i;
    }
    S=v[d[pr]];
    for(i=2;i<=n-k+1;i++)
    {
        if(d[pr]==i-1) pr++;
        while(pr<=ul&&v[d[ul]]>=v[i+k-1])
            ul--;
        ul++;
        d[ul]=i+k-1;
        S=S+v[d[pr]];
    }
    fout<<S;
    fin.close();
    fout.close();
    return 0;
}