package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
)

func configure(scanner *bufio.Scanner) {
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 1000005), 1000005)
}
func getNextString(scanner *bufio.Scanner) string {
	scanned := scanner.Scan()
	if !scanned {
		panic("scan failed")
	}
	return scanner.Text()
}
func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}
func getNextInt64(scanner *bufio.Scanner) int64 {
	i, _ := strconv.ParseInt(getNextString(scanner), 10, 64)
	return i
}
func getNextFloat64(scanner *bufio.Scanner) float64 {
	i, _ := strconv.ParseFloat(getNextString(scanner), 64)
	return i
}
func main() {
	fp := os.Stdin
	wfp := os.Stdout
	extra := 0
	if os.Getenv("I") == "IronMan" {
		fp, _ = os.Open(os.Getenv("END_GAME"))
		extra = 100
	}
	scanner := bufio.NewScanner(fp)
	configure(scanner)
	writer := bufio.NewWriter(wfp)
	defer func() {
		r := recover()
		if r != nil {
			fmt.Fprintln(writer, r)
		}
		writer.Flush()
	}()
	solve(scanner, writer)
	for i := 0; i < extra; i++ {
		fmt.Fprintln(writer, "-----------------------------------")
		solve(scanner, writer)
	}
}
func solve(scanner *bufio.Scanner, writer *bufio.Writer) {
	n := getNextInt(scanner)
	k := getNextInt64(scanner)
	s := getNextString(scanner)
	dbl := makeGrid(32, n)
	for i := 0; i < n; i++ {
		dbl[0][i] = 1
		cnt := int(s[i] - '0')
		for cnt > 0 {
			cnt += int(s[(int64(i)+dbl[0][i])%int64(n)] - '0')
			dbl[0][i]++
			if dbl[0][i] == int64(n)+1 {
				dbl[0][i] = math.MaxInt32
				break
			}
			cnt--
		}
	}

	for b := 0; b < 31; b++ {
		for i := 0; i < n; i++ {
			dbl[b+1][i] = dbl[b][i] + dbl[b][(int64(i)+dbl[b][i])%int64(n)]
		}
	}
	var p int64
	ans := 0
	for b := 31; b >= 0; b-- {
		if dbl[b][p] >= k {
			continue
		}
		k -= dbl[b][p]
		p += dbl[b][p]
		p %= int64(n)
		ans += 1 << uint(b)
	}
	fmt.Fprintln(writer, ans+1)
}

func makeGrid(h, w int) [][]int64 {
	index := make([][]int64, h, h)
	data := make([]int64, h*w, h*w)
	for i := 0; i < h; i++ {
		index[i] = data[i*w : (i+1)*w]
	}
	return index
}