using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    private int N, K;
    private int[] A;

    public void Solve()
    {
        var sc = new Scanner();
        N = sc.NextInt();
        K = sc.NextInt();
        A = sc.IntArray();

        // [0,i)の和 - i をKで割ったあまり
        var s = new long[N + 1];
        for (int i = 0; i < N; i++)
        {
            s[i + 1] = s[i] + A[i] - 1;
            s[i + 1] %= K;
            if (s[i + 1] < 0) s[i + 1] += K;
        }

        // [l,r)が条件満たす
        // s[r]-s[l] ==0
        var map = new HashMap<long, int>();
        long ans = 0;
        for (int i = 0; i <= N; i++)
        {
            var c = map[s[i]];
            ans += c;
            map[s[i]]++;

            if (i - K + 1 >= 0)
                map[s[i - K + 1]]--;
        }

        Console.WriteLine(ans);
    }


    public static void Main(string[] args)
    {
        new Program().Solve();
    }
}

class HashMap<K, V> : Dictionary<K, V>
{
    new public V this[K i]
    {
        get
        {
            V v;
            TryGetValue(i, out v);
            return v;
        }
        set { base[i] = value; }
    }
}

struct E
{
    public int B, Index;

    public E(int b, int i)
    {
        B = b;
        Index = i;
    }
}


class Scanner
{
    public Scanner()
    {
        _pos = 0;
        _line = new string[0];
    }

    const char Separator = ' ';
    private int _pos;
    private string[] _line;

    #region スペース区切りで取得

    public string Next()
    {
        if (_pos >= _line.Length)
        {
            _line = Console.ReadLine().Split(Separator);
            _pos = 0;
        }

        return _line[_pos++];
    }

    public int NextInt()
    {
        return int.Parse(Next());
    }

    public long NextLong()
    {
        return long.Parse(Next());
    }

    public double NextDouble()
    {
        return double.Parse(Next());
    }

    #endregion

    #region 型変換

    private int[] ToIntArray(string[] array)
    {
        var result = new int[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = int.Parse(array[i]);
        }

        return result;
    }

    private long[] ToLongArray(string[] array)
    {
        var result = new long[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = long.Parse(array[i]);
        }

        return result;
    }

    private double[] ToDoubleArray(string[] array)
    {
        var result = new double[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = double.Parse(array[i]);
        }

        return result;
    }

    #endregion

    #region 配列取得

    public string[] Array()
    {
        if (_pos >= _line.Length)
            _line = Console.ReadLine().Split(Separator);

        _pos = _line.Length;
        return _line;
    }

    public int[] IntArray()
    {
        return ToIntArray(Array());
    }

    public long[] LongArray()
    {
        return ToLongArray(Array());
    }

    public double[] DoubleArray()
    {
        return ToDoubleArray(Array());
    }

    #endregion
}

Measured memory_bytes: 47076