#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;
int cmp(void const *a, void const *b);
int fun();
struct data
{
double b;
double e;
};
data a[110];
int n;
int main()
{
while(cin >> n)
{
int h1, m1, h2, m2;
for(int i = 1; i <= n; i++)
{
double t1, t2;
scanf("%d:%d-%d:%d", &h1, &m1, &h2, &m2);
t1 = h1 + m1/60.0;
t2 = h2 + m2/60.0;
a[i].b = t1 < t2 ? t1 : t2;
a[i].e = t1 > t2 ? t1 : t2;
}
qsort(a+1, n, sizeof(a[0]), cmp);
cout << fun() << endl;
}
}
int fun()
{
double cur;
int num = 1;
cur = a[1].e;
for(int i = 2; i <= n; i++)
{
if(a[i].b <= cur && a[i].e >= cur)
{
continue;
}
else
{
cur = a[i].e;
num++;
}
}
return num;
}
int cmp(void const *a, void const *b)
{
if( ((data *)a)->e >= ((data *)b)->e )
return 1;
else
return -1;
}