#include <bits/stdc++.h>
#define pb push_back

using namespace std;

class Parser {
  private:
    static const int SIZE = 1e5;
    char str[SIZE];

    int ptr;
    FILE *fin;

    char getChar() {
        if (ptr == SIZE) {
            fread(str, sizeof(char), SIZE, fin);
            ptr = 0;
        }
        return str[ptr++];
    }

    int getInt() {
        char chr = getChar();
        while (!isdigit(chr) && chr != '-')
            chr = getChar();

        int sgn = +1;
        if (chr == '-') {
            sgn = -1;
            chr = getChar();
        }

        int nr = 0;
        while (isdigit(chr)) {
            nr = nr * 10 + chr - '0';
            chr = getChar();
        }
        return nr * sgn;
    }

  public:
    Parser(const char* str) :
        ptr(SIZE), fin(fopen(str, "r")) { }

    ~Parser() {
        fclose(fin);
    }

    friend Parser& operator>>(Parser& in, int& nr) {
        nr = in.getInt();
        return in;
    }
};

Parser fin("deque.in");
ofstream fout("deque.out");

void debug_out() { cerr << '\n'; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) { cerr << " " << H; debug_out(T...);}
#define dbg(...) cerr << #__VA_ARGS__ << " ->", debug_out(__VA_ARGS__)
#define dbg_v(x, n) do{cerr<<#x"[]: ";for(int _=0;_<n;++_)cerr<<x[_]<<" ";cerr<<'\n';}while(0)
#define dbg_ok cerr<<"OK!\n"

typedef pair<int,int> pii;
typedef long long int ll;
typedef long double ld;

const int DMAX = 1e5+10;

deque <pii> deq;

int n,k;
ll ans;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int i,x;

    fin>>n>>k;
    for(i=1;i<=k;i++){
        fin>>x;
        while(!deq.empty() && deq.back().first >= x)
            deq.pop_back();
        deq.push_back({x,i});
    }
    ans+=deq.front().first;
    for(i=k+1;i<=n;i++){
        fin>>x;
        if(deq.front().second <= i-k)
            deq.pop_front();
        while(!deq.empty() && deq.back().first >= x)
            deq.pop_back();
        deq.push_back({x,i});
        ans+=deq.front().first;
    }
    fout<<ans<<'\n';
    return 0;
}