/*
Contest : CF GYM
*/

#include<bits/stdc++.h>
using namespace std;

typedef long long int LL;

#define inp_s     ios_base::sync_with_stdio(false);cin.tie(0)
#define DRT()     int test_case;cin>>test_case;while(test_case--)

#define VI        vector<int>
#define VS        vector<string>
#define VLL       vector<LL>
#define PII       pair<int,int>

#define all(c)    c.begin(),c.end()
#define sz(c)     c.size()
#define clr(c)    c.clear()
#define pb        push_back
#define mp        make_pair

#define GI(x)     scanf("%d",&x)
#define endn    "\n"

#define FOR(i,a,b)      for(int i=a;i<b;i++)
#define RFOR(i,a,b)     for(int i=b-1;i>=a;i--)

#define gcd(a,b)  __gcd(a,b)
#define MOD       1000000007
#define EPS       1E-10
#define PI      acos(-1)

#define CASE(x)   cout << "Case #" << x << ": ";

LL getTime(string x)
{
    int hh = (x[0] - '0') * 10 + x[1] - '0';
    int mm = (x[3] - '0') * 10 + x[4] - '0';
    int ss = (x[6] - '0') * 10 + x[7] - '0';
    LL ret = ss + (mm*60) + (hh*3600);
    return ret;
}

int main()
{
    inp_s;
    int n;
    cin >> n;
    VLL arr(n);
    FOR(i,0,n)
    {
        string s;
        cin >> s;
        arr[i] = getTime(s);
    }
    sort(all(arr));
    int ans = 1;
    priority_queue < LL , VLL , greater<LL> > pq;
    pq.push(arr[0] + 900);
    FOR(i,1,n)
    {
        LL minFree = pq.top();
        LL answer_min = arr[i];
        LL answer_max = arr[i] + 3 * 60 * 60 - 900;
        if(minFree > answer_max)
        {
            ans += 1;
            pq.push(answer_min + 900);
        }
        else if(minFree < answer_min)
        {
            pq.pop();
            pq.push(answer_min + 900);
        }
        else
        {
            pq.pop();
            pq.push(minFree + 900);
        }
    }

    cout << ans << endl;
    return 0;
}