#include <stdio.h>
#include <stdlib.h>

#define MAXN 5000000

int coada[ MAXN ], a[ MAXN ];

int main()
{
    FILE *fin, *fout;
    int n, k, i, left = 0, right = -1;
    long long suma = 0;
    fin = fopen( "deque.in", "r" );

    fscanf( fin, "%d%d", &n, &k );
    for( i = 0; i < n; i++ )
    {
        fscanf( fin, "%d", &a[ i ] );
        while( left <= right && a[ i ] <= a[ coada[ right ] ] )
        {
            right--;
        }

        if( left <= right && coada[ left ] == i - k )
        {
            left++;
        }

        coada[ ++right ] = i;
        if( i >= k - 1 )
        {
            suma += a[ coada[ left ] ];
        }
    }
    fclose( fin );

    fout = fopen( "deque.out", "w" );
    fprintf( fout, "%lld\n", suma );
    fclose( fout );

    return 0;
}