import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.NoSuchElementException;

class Edge{
	int dst;
	long cost;
	
	public Edge(int dst,long cost) {
		this.dst=dst;
		this.cost=cost;
	}
}

public class Main {
	public static void main(String[] args) throws FileNotFoundException {
		long t = System.currentTimeMillis();
		new Main().run();
		System.err.println(System.currentTimeMillis() - t);
	}
	
	void run() {
		FastScanner sc = new FastScanner();
		int N=sc.nextInt();
		long K=sc.nextLong();
		char[] cs=sc.next().toCharArray();
		long[][] dp=new long[N][32];
		for(int i=0;i<cs.length;++i) {
			int p=i;
			int res=1;
			while(res>0&&p-i<=N) {
				res=res-1+(int)(cs[p%N]-'0');
				++p;
			}
			dp[i][0]=(p-i)==(N+1)?(K+1):(p-i);
		}
		for(int i=0;i+1<32;++i) {
			for(int j=0;j<N;++j) {
				if(dp[j][i]==K+1)dp[j][i+1]=dp[j][i];
				else {
					int npos=(int)((j+dp[j][i])%N);
					dp[j][i+1]=dp[j][i]+dp[npos][i];
				}
			}
		}
		long ans=0,res=K;
		int pos=0;
		while(res>0) {
			int p=0;
			while(dp[pos][p+1]<res)++p;
			ans+=1L<<p;
			res-=dp[pos][p];
			pos=(int) ((pos+dp[pos][p])%N);
		}
		System.out.println(ans);
	}

	
	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}
	
	
class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
    private void skipUnprintable() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;}
    public boolean hasNext() { skipUnprintable(); return hasNextByte();}
    public String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while(isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }
    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
    
    public int nextInt() {
    	return (int)nextLong();
    }
}