import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


alias Pair = Tuple!(int, "a", int, "b");

int readTime() {
  const d = readInt();
  const hhmm = readToken();
  const hh = hhmm[0 .. 2].to!int;
  const mm = hhmm[3 .. 5].to!int;
  return (d * 60 + hh) * 60 + mm;
}

void main() {
  try {
    for (; ; ) {
      const N = readInt();
      const M = readInt();
      auto P = new Pair[M];
      foreach (i; 0 .. M) {
        P[i].a = readTime();
        P[i].b = readTime();
      }
      debug {
        writeln("P = ", P);
      }
      
      P.sort!"a.b < b.b";
      auto set = (-1).repeat(N).redBlackTree!true;
      debug {
        writeln("set = ", set);
      }
      int ans;
      foreach (i; 0 .. M) {
        auto ran = set.lowerBound(P[i].a);
        if (!ran.empty) {
          const b = ran.back;
          ++ans;
          set.removeKey(b);
          set.insert(P[i].b);
        }
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}