#include<algorithm>
#include<bitset>
#include<cmath>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<deque>
#include<fstream>
#include<iomanip>
#include<iostream>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<unordered_map>
#include<unordered_set>
#include<utility>
#include<vector>

using namespace std;

#ifdef HOME
const string inputFile = "input.txt";
const string outputFile = "output.txt";
#else
const string problemName = "deque";
const string inputFile = problemName + ".in";
const string outputFile = problemName + ".out";
#endif

typedef pair<int, int> PII;
typedef long long int lld;

int N, K;
deque<PII> D;
lld sum;

int main() {
    int i, x;

#ifndef ONLINE_JUDGE
    freopen(inputFile.c_str(), "r", stdin);
    freopen(outputFile.c_str(), "w", stdout);
#endif

    scanf("%d%d", &N, &K);

    for(i = 1; i <= K; i++) {
        scanf("%d", &x);

        while(!D.empty() && D.back().second > x)
            D.pop_back();

        D.push_back(make_pair(i, x));
    }

    sum = D.front().second;

    for(; i <= N; i++) {
        scanf("%d", &x);

        while(!D.empty() && i - D.front().first + 1 > K)
            D.pop_front();

        while(!D.empty() && D.back().second > x)
            D.pop_back();

        D.push_back(make_pair(i, x));

        sum += D.front().second;
    }

    printf("%lld\n", sum);

    return 0;
}