#include<stdio.h>
#include<deque>

using namespace std;

const int NMAX = 5000000;

struct str
{
    int val, poz;
}v[NMAX+1];

deque<str> d;

int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    
    int n, k;
    long long sol=0ll;
    
    scanf("%d%d", &n, &k);
    
    for(int i=1; i<=n; ++i)
    {
        scanf("%d", &v[i].val);
        
        v[i].poz=i;
    }
    
    for(int i=1; i<k; ++i)
    {
        while(d.size() && d.back().val>=v[i].val)
            d.pop_back();
        
        d.push_back(v[i]);
    }
    
    for(int i=k; i<=n; ++i)
    {
        if(d.front().poz<=i-k)
            d.pop_front();
        
        while(d.size() && d.back().val>=v[i].val)
            d.pop_back();
        
        d.push_back(v[i]);
        
        sol+=(long long)d.front().val;
    }
    
    printf("%lld\n", sol);
    
    return 0;
}