#include <queue>
#include <fstream>
#include <cstdlib>
#define N_MAX 5000011
#define bufferSize 8192

using namespace std;
int v[N_MAX];
int bufferIndex;
char buffer[bufferSize];
deque< int > dQ;
inline void read( istream& in, int& x )
{
	if( -1 == bufferIndex )
	{
		in.read( buffer, bufferSize );
		bufferIndex=0;
	}
	int sgn=1;
	while( buffer[bufferIndex] < '0' || buffer[bufferIndex] > '9' )
	{
		if( '-' == buffer[bufferIndex] )
			sgn*=-1;
		if( ++bufferIndex == bufferSize )
		{
			in.read( buffer, bufferSize );
			bufferIndex=0;
		}
	}
	for( x=0; buffer[bufferIndex] >= '0' && buffer[bufferIndex] <= '9'; )
	{
		x=x*10+buffer[bufferIndex]-'0';
		if( ++bufferIndex == bufferSize )
		{
			in.read( buffer, bufferSize );
			bufferIndex=0;
		}
	}
	x*=sgn;
}
int main( void )
{
	int N, K, i;
	long long int s=0;
	ifstream in( "deque.in" );
	read(in, N); read(in, K);
	for( i=1; i <= N; ++i )
	{
		read(in, v[i] );
		for( ; !dQ.empty() && v[dQ.back()] >= v[i]; dQ.pop_back() );
		dQ.push_back(i);
		if( i >= K )
			s+=v[dQ.front()];
		if( i-K+1 == dQ.front() )
			dQ.pop_front();
	}
	ofstream out( "deque.out" );
	out<<s<<'\n';
	return EXIT_SUCCESS;
}