import java.io.*; import java.util.*; public class Main_yukicoder580 { private static Scanner sc; private static Printer pr; private static void solve() { int n = sc.nextInt(); int m = sc.nextInt(); int[] in = new int[m]; int[] out = new int[m]; // int max = 60 * 24 * 9; for (int i = 0; i < m; i++) { int d = sc.nextInt(); String[] hm = sc.next().split(":"); int o = sc.nextInt(); String[] ohm = sc.next().split(":"); in[i] = d * 60 * 24 + Integer.parseInt(hm[0]) * 60 + Integer.parseInt(hm[1]); out[i] = o * 60 * 24 + Integer.parseInt(ohm[0]) * 60 + Integer.parseInt(ohm[1]) + 1; } List list = new ArrayList<>(m); for (int i = 0; i < m; i++) { list.add(i); } Collections.sort(list, (o1, o2) -> {if (out[o1] == out[o2]) return Integer.compare(in[o2], in[o1]); else return Integer.compare(out[o1], out[o2]);}); PriorityQueue pq = new PriorityQueue<>(Collections.reverseOrder()); for (int i = 0; i < n; i++) { pq.add(0); } int ans = 0; out: for (int e : list) { List tmp = new ArrayList<>(); while (!pq.isEmpty()) { int ee = pq.remove(); if (ee > in[e]) { tmp.add(ee); } else { pq.add(out[e]); pq.addAll(tmp); continue out; } } pq.addAll(tmp); ans++; } pr.println(m - ans); } // --------------------------------------------------- public static void main(String[] args) { sc = new Scanner(System.in); pr = new Printer(System.out); solve(); pr.close(); sc.close(); } @SuppressWarnings("unused") private static class Scanner { BufferedReader br; Scanner (InputStream in) { br = new BufferedReader(new InputStreamReader(in)); } private boolean isPrintable(int ch) { return ch >= '!' && ch <= '~'; } private boolean isCRLF(int ch) { return ch == '\n' || ch == '\r' || ch == -1; } private int nextPrintable() { try { int ch; while (!isPrintable(ch = br.read())) { if (ch == -1) { throw new NoSuchElementException(); } } return ch; } catch (IOException e) { throw new NoSuchElementException(); } } String next() { try { int ch = nextPrintable(); StringBuilder sb = new StringBuilder(); do { sb.appendCodePoint(ch); } while (isPrintable(ch = br.read())); return sb.toString(); } catch (IOException e) { throw new NoSuchElementException(); } } int nextInt() { try { // parseInt from Integer.parseInt() boolean negative = false; int res = 0; int limit = -Integer.MAX_VALUE; int radix = 10; int fc = nextPrintable(); if (fc < '0') { if (fc == '-') { negative = true; limit = Integer.MIN_VALUE; } else if (fc != '+') { throw new NumberFormatException(); } fc = br.read(); } int multmin = limit / radix; int ch = fc; do { int digit = ch - '0'; if (digit < 0 || digit >= radix) { throw new NumberFormatException(); } if (res < multmin) { throw new NumberFormatException(); } res *= radix; if (res < limit + digit) { throw new NumberFormatException(); } res -= digit; } while (isPrintable(ch = br.read())); return negative ? res : -res; } catch (IOException e) { throw new NoSuchElementException(); } } long nextLong() { try { // parseLong from Long.parseLong() boolean negative = false; long res = 0; long limit = -Long.MAX_VALUE; int radix = 10; int fc = nextPrintable(); if (fc < '0') { if (fc == '-') { negative = true; limit = Long.MIN_VALUE; } else if (fc != '+') { throw new NumberFormatException(); } fc = br.read(); } long multmin = limit / radix; int ch = fc; do { int digit = ch - '0'; if (digit < 0 || digit >= radix) { throw new NumberFormatException(); } if (res < multmin) { throw new NumberFormatException(); } res *= radix; if (res < limit + digit) { throw new NumberFormatException(); } res -= digit; } while (isPrintable(ch = br.read())); return negative ? res : -res; } catch (IOException e) { throw new NoSuchElementException(); } } float nextFloat() { return Float.parseFloat(next()); } double nextDouble() { return Double.parseDouble(next()); } String nextLine() { try { int ch; while (isCRLF(ch = br.read())) { if (ch == -1) { throw new NoSuchElementException(); } } StringBuilder sb = new StringBuilder(); do { sb.appendCodePoint(ch); } while (!isCRLF(ch = br.read())); return sb.toString(); } catch (IOException e) { throw new NoSuchElementException(); } } void close() { try { br.close(); } catch (IOException e) { // throw new NoSuchElementException(); } } } private static class Printer extends PrintWriter { Printer(PrintStream out) { super(out); } } }