#include <algorithm>
#include <cstdio>
#include <cctype>
#include <deque>

using namespace std;

namespace FastIO
{
    char buf[1<<21], *p1=buf, *p2=buf;
    void read () {}
    inline int getch (void)
    {
        return p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++;
    }
    template <typename T, typename... G> void read (T &x, G &... o)
    {
        int f = 1, ch = getch(); x = 0;
        while(!isdigit(ch))
        {
            if(ch == '-')
                f = -f;
            ch = getch();
        }
        while(isdigit(ch))
        {
            x = x * 10 + ch - '0';
            ch = getch();
        }
        x = x * f;
        read(o...);
    }
}

#define read FastIO::read

struct node
{
    int id;
    long long x;
};

deque < node > q;

const int maxn = 1000005;

int n, m, a[maxn];
long long f[maxn];

int main (void)
{
    read(n,m);
    for(register int i=1; i<=n; ++i)
        read(a[i]);
    for(register int i=1; i<=m; ++i)
    {
        f[i] = a[i];
        while (!q.empty() && q.back().x>f[i]) q.pop_back();
        q.push_back((node){i, f[i]});
    }
    for(register int i=m+1; i<=n; ++i)
    {
        while (!q.empty() && q.front().id+m<i) q.pop_front();
        f[i] = q.front().x + a[i];
        while (!q.empty() && q.back().x>f[i]) q.pop_back();
        q.push_back((node){i, f[i]});
    }
    long long ans = 1ll<<60;
    for(register int i=n; i>=n-m+1; --i)
        ans = min(ans, f[i]);
    printf("%lld\n", ans);
    return 0;
}

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