#include <fstream>
#include <cstdio>
#include <deque>
#include <vector>

using namespace std;

deque<int> d;

vector<int> v;
FILE *fin = fopen("deque.in","r");
FILE *fout = fopen("deque.out","w");
long long sol;
int i,n,k,x;

int main() {
    fscanf(fin,"%d%d",&n,&k);
    for (i=1;i<=n;i++) {
        fscanf(fin,"%d",&x);
        v.push_back(x);
    }

    for (i=0;i<n;i++) {
        while (!d.empty() && v[i] <= v[d.back()])
            d.pop_back();
        d.push_back(i);
        if (i-d.front() == k)
            d.pop_front();
        if (i>=k-1)
            sol+=v[d.front()];
    }
    fprintf(fout,"%lld\n",sol);
    return 0;
}