package q1xx; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.Arrays; import java.util.InputMismatchException; public class Q183_2 { static InputStream is; static PrintWriter out; static String INPUT = ""; static void solve() { int n = ni(), L = ni()*60; int[] len = new int[n]; int sum = 0; for(int i = 0;i < n;i++){ len[i] = ni()*60+ni(); sum += len[i]; } if(L >= sum){ out.println(n); return; } double[] f = new double[60]; f[0] = 1; for(int i = 1;i < 60;i++)f[i] = f[i-1] * i; long[][] dp = new long[n+1][3600*n+1]; dp[0][0] = 1; for(int i = 0;i < n;i++){ for(int j = i;j >= 0;j--){ for(int k = 3600*i;k >= 0;k--){ int nj = j+1; int nk = k+len[i]; dp[nj][nk] += dp[j][k]; } } } double ret = 0; double e = 0; for(int last = 0;last < n;last++){ for(int j = 0;j <= n-1;j++){ for(int k = 0;k <= 3600*n-len[last];k++){ int nj = j+1; int nk = k+len[last]; dp[nj][nk] -= dp[j][k]; } } for(int i = 0;i < n;i++){ long sumk = 0; for(int k = L-1;k >= L-len[last] && k >= 0;k--){ sumk += dp[i][k]; } e += (double)(i+1)*sumk*f[i]*f[n-1-i]; } for(int j = n-1;j >= 0;j--){ for(int k = 3600*n-len[last];k >= 0;k--){ int nj = j+1; int nk = k+len[last]; dp[nj][nk] += dp[j][k]; } } } out.printf("%.12f\n", e/f[n]+ret); } public static void main(String[] args) throws Exception { long S = System.currentTimeMillis(); is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes()); out = new PrintWriter(System.out); solve(); out.flush(); long G = System.currentTimeMillis(); tr(G-S+"ms"); } private static boolean eof() { if(lenbuf == -1)return true; int lptr = ptrbuf; while(lptr < lenbuf)if(!isSpaceChar(inbuf[lptr++]))return false; try { is.mark(1000); while(true){ int b = is.read(); if(b == -1){ is.reset(); return true; }else if(!isSpaceChar(b)){ is.reset(); return false; } } } catch (IOException e) { return true; } } private static byte[] inbuf = new byte[1024]; static int lenbuf = 0, ptrbuf = 0; private static int readByte() { if(lenbuf == -1)throw new InputMismatchException(); if(ptrbuf >= lenbuf){ ptrbuf = 0; try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); } if(lenbuf <= 0)return -1; } return inbuf[ptrbuf++]; } private static boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); } private static int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; } private static double nd() { return Double.parseDouble(ns()); } private static char nc() { return (char)skip(); } private static String ns() { int b = skip(); StringBuilder sb = new StringBuilder(); while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ') sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } private static char[] ns(int n) { char[] buf = new char[n]; int b = skip(), p = 0; while(p < n && !(isSpaceChar(b))){ buf[p++] = (char)b; b = readByte(); } return n == p ? buf : Arrays.copyOf(buf, p); } private static char[][] nm(int n, int m) { char[][] map = new char[n][]; for(int i = 0;i < n;i++)map[i] = ns(m); return map; } private static int[] na(int n) { int[] a = new int[n]; for(int i = 0;i < n;i++)a[i] = ni(); return a; } private static int ni() { int num = 0, b; boolean minus = false; while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')); if(b == '-'){ minus = true; b = readByte(); } while(true){ if(b >= '0' && b <= '9'){ num = num * 10 + (b - '0'); }else{ return minus ? -num : num; } b = readByte(); } } private static long nl() { long num = 0; int b; boolean minus = false; while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')); if(b == '-'){ minus = true; b = readByte(); } while(true){ if(b >= '0' && b <= '9'){ num = num * 10 + (b - '0'); }else{ return minus ? -num : num; } b = readByte(); } } private static void tr(Object... o) { if(INPUT.length() != 0)System.out.println(Arrays.deepToString(o)); } }