import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[]args) throws Throwable {
		double fac[] = new double[60];
		int maxSum = 25500;
		double dp1[][] = new double[maxSum + 10][60];
		double dp2[][] = new double[maxSum + 10][60];
		fac[0] = 1;
		for (int i = 1 ; i < 60 ; ++i) {
			fac[i] = 1.0*i * fac[i - 1];
		}
		int s[] = new int[60];
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt(), l = sc.nextInt();
		long sum = 0;
		l*=60;

		for (int i = 0 ; i < n ; ++i) {
			String str = sc.next();
			StringTokenizer st = new StringTokenizer(str,":");
			int x = new Integer(st.nextToken()), y=  new Integer(st.nextToken());
			s[i]=x*60+y;
			sum+=s[i];
		}
		if (l >= sum) {
			System.out.println(n);
			return;
		}

		dp1[0][0] = 1;
		for (int i = 0 ; i < n ; ++i) {
			for (int j = i; j >= 0 ; --j) {
				for (int cur = 0; cur <= maxSum ; ++cur) {

					dp1[Math.min(maxSum,cur + s[i])][j + 1] += 1.0*dp1[cur][j];
				}
			}
		}
		double ways = 0.0;
		for (int i = 0 ; i < n ; ++i) {
			for (int j = 0 ; j < n ; ++j) {
				for (int cur = 0 ; cur < l ;++cur) {
					dp2[cur][j] = dp1[cur][j];
					if (cur - s[i] >= 0 && j >= 1) {
						dp2[cur][j] -= dp2[cur - s[i]][j - 1];
					}
					if (j < n && cur + s[i] >= l) {
						ways += 1.0*(j+1)*(((dp2[cur][j] * 1.0*fac[j] * fac[n - j - 1])));
					}

				}
			}
		}

		System.out.printf("%.15f\n",ways/fac[n]);


	}

	static class Scanner {
		StringTokenizer st;
		BufferedReader br;

		public Scanner(InputStream s) {
			br = new BufferedReader(new InputStreamReader(s));
		}

		public Scanner(String s) throws FileNotFoundException {
			br = new BufferedReader(new FileReader(new File(s)));
		}

		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}

		public int nextInt() throws IOException {
			return Integer.parseInt(next());
		}

		public long nextLong() throws IOException {
			return Long.parseLong(next());
		}

		public String nextLine() throws IOException {
			return br.readLine();
		}

		public double nextDouble() throws IOException {
			return Double.parseDouble(next());
		}

		public boolean ready() throws IOException {
			return br.ready();
		}
	}
}