#include <cstdio>
#include <deque>
using namespace std;

FILE * in= fopen("deque.in","r");
FILE * out= fopen("deque.out","w");

int main()
{
    long long sum=0;
    int n,k;
    fscanf(in,"%d%d",&n,&k);
    deque <pair<int,int>> d;
    for(int i=0; i<n; i++)
    {
        int x;
        fscanf(in,"%d",&x);
        while(!d.empty()&&(d.back().first>x))
            d.pop_back();
        d.push_back({x,i});
        if(d.front().second <= i-k)
            d.pop_front();
        if(i >= k-1)
            sum+=d.front().first;
    }
    fprintf(out,"%lld",sum);
    return 0;
}