///just wondering how this is faster than mine..

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

using namespace std;

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

#define BUF 1 << 17
char buf[BUF];
int pos = BUF;

inline char next()  {
    if(pos == BUF)
        fread(buf, 1, BUF, fin), pos = 0;
    return buf[pos++];
}

inline int read()  {
    int x = 0, semn = 1;
    char ch = next();
    while(!isdigit(ch) && ch != '-')
        ch = next();
    if(ch == '-')
        ch = next(), semn = -1;
    while(isdigit(ch))
        x = x * 10 + ch - '0', ch = next();
    return x * semn;
}

#define MAXN 5000001

deque <int> q;

int N, K;
int v[MAXN];long long sum;

int main()  {
    N = read(), K = read();
    for(int i = 1;i <= N;i++)  {
        v[i] = read();
    }
    for(int i = 1;i <= N;i++)  {
        while(!q.empty() && v[i] <= v[q.back()])
            q.pop_back();
        q.push_back(i);
        if(q.front() == i - K)
            q.pop_front();
        if(i >= K)
            sum += 1LL * v[q.front()];
    }
    fprintf(fout, "%lld", sum);
    fclose(fin);
    fclose(fout);
    return 0;
}