void main(){
  import std.stdio, std.string, std.conv, std.algorithm;
  import std.typecons, std.container;
  
  int n, m; rd(n, m);
  auto seq=new Tuple!(int, int)[](m);
  foreach(i; 0..m){
    int d1, d2;
    string t1, t2;
    rd(d1, t1, d2, t2);
    auto st=d1*24*60+to!(int)(t1[0..2])*60+to!(int)(t1[3..$]);
    auto ed=d2*24*60+to!(int)(t2[0..2])*60+to!(int)(t2[3..$]);
    seq[i]=Tuple!(int, int)(st, ed);
  }
  
  sort!"a[1]<b[1]"(seq);

  alias P=Tuple!(int, int);
  auto Q=new BinaryHeap!(Array!P, "a[0]>a[1]");
  auto sum=0;
  foreach(e; seq){
    while(Q.length>0 && Q.front[1]<e[0]) Q.removeFront;
    if(Q.length<n)Q.insert(P(e)), sum++;
  }
  writeln(sum);
}

void rd(T...)(ref T x){
  import std.stdio, std.string, std.conv;
  auto l=readln.split;
  assert(l.length==x.length);
  foreach(i, ref e; x){
    e=l[i].to!(typeof(e));
  }
}