////////////////////////////////////////
///  tu3 pro-con template            ///
////////////////////////////////////////
#include <cassert>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <iostream>
#include <sstream>
#include <algorithm>
#include <numeric>
#include <functional>
#include <vector>
#include <queue>
#include <string>
#include <complex>
#include <stack>
#include <set>
#include <map>
#include <list>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <regex>
using namespace std;

//// MACRO ////
#define countof(a) (sizeof(a)/sizeof(a[0]))

#define REP(i,n) for (int i = 0; i < (n); i++)
#define RREP(i,n) for (int i = (n)-1; i >= 0; i--)
#define FOR(i,s,n) for (int i = (s); i < (n); i++)
#define RFOR(i,s,n) for (int i = (n)-1; i >= (s); i--)
#define pos(c,i) c.being() + (i)
#define allof(c) c.begin(), c.end()
#define aallof(a) a, countof(a)
#define partof(c,i,n) c.begin() + (i), c.begin() + (i) + (n)
#define apartof(a,i,n) a + (i), a + (i) + (n)
#define long long long

#define EPS 1e-9
#define INF (1L << 30)
#define LINF (1LL << 60)

#define PREDICATE(t,a,exp) [&](const t & a) -> bool { return exp; }
#define COMPARISON_T(t) bool(*)(const t &, const t &)
#define COMPARISON(t,a,b,exp) [&](const t & a, const t & b) -> bool { return exp; }
#define CONVERTER(TSrc,t,TDest,exp) [&](const TSrc &t)->TDest { return exp; }

inline int sign(double x) { return (abs(x) < EPS ? 0 : x > 0 ? 1 : -1); }
inline bool inRange(int val, int min, int max) { return val >= min && val < max; }
inline bool inRange(double val, double min, double max) { return val - min > -EPS && val - max < EPS; }
template <class T> struct vevector : public vector<vector<T>> { vevector(int n = 0, int m = 0, const T &initial = T()) : vector<vector<T>>(n, vector<T>(m, initial)) { } };
template <class T> struct vevevector : public vector<vevector<T>> { vevevector(int n = 0, int m = 0, int l = 0, const T &initial = T()) : vector<vevector<T>>(n, vevector<T>(m, l, initial)) { } };
template <class T> struct vevevevector : public vector<vevevector<T>> { vevevevector(int n = 0, int m = 0, int l = 0, int k = 0, const T &initial = T()) : vector<vevevector<T>>(n, vevevector<T>(m, l, k, initial)) { } };
inline bool contains(int x, int y, int W, int H) { return x >= 0 && x < W && y >= 0 && y < H; } // W,H含まない

//// i/o helper ////

#ifdef _DEBUG
#define DEBUG WRITE
inline void readfrom(string filename) { freopen(filename.c_str(), "r", stdin); }
inline void writeto(string filename) { freopen(filename.c_str(), "w", stdout); }
#else
#define DEBUG(...)
inline void readfrom(...) { }
inline void writeto(...) { }
#endif
#ifdef ccout
#  define cout ccout
#  define endl cendl
#endif

struct _Reader { template <class T> _Reader operator ,(T &rhs) { cin >> rhs; return *this; } };
struct _Writer { bool f; _Writer() : f(false) { } template <class T> _Writer operator ,(const T &rhs) { cout << (f ? " " : "") << rhs; f = true; return *this; } };
#define READ(t,...) t __VA_ARGS__; _Reader(), __VA_ARGS__
#define WRITE(...) _Writer(), __VA_ARGS__; cout << endl

template <class T> T read() { T t; cin >> t; return t; }
template <class T> vector<T> read(int n) { vector<T> v; REP(i, n) { v.push_back(read<T>()); } return v; }
template <class T> vevector<T> read(int n, int m) { vevector<T> v; REP(i, n) v.push_back(read<T>(m)); return v; }
template <class T> vevector<T> readjag() { return read<T>(read<int>()); }
template <class T> vevector<T> readjag(int n) { vevector<T> v; REP(i, n) v.push_back(readjag<T>()); return v; }

template <class T1, class T2> inline istream & operator >> (istream & in, pair<T1, T2> &p) { in >> p.first >> p.second; return in; }
template <class T1, class T2> inline ostream & operator << (ostream &out, pair<T1, T2> &p) { out << p.first << p.second; return out; }
template <class T> inline ostream & operator << (ostream &out, const vector<T> &v)
{
	ostringstream ss;
	for (auto x : v) ss << x << ' ';
	auto s = ss.str();
	out << s.substr(0, s.length() - 1) << endl;
	return out;
}

//// start up ////
void solve();


int main()
{
	solve();
	return 0;
}

////////////////////
/// template end ///
////////////////////

void solve()
{
	int testcases = INF;
	REP(testcase, testcases)
	{
		READ(int, n);
		if (!(n)) break;
		
		vector<int> checkin(1000);
		vector<int> endowed(1000);

		REP(i, n)
		{
			int h, m, id;
			scanf("%*s%d:%d %*c %d", &h, &m, &id);
			
			int cur = h * 60 + m;
			if (!checkin[id]) { checkin[id] = cur; }
			else
			{
				if (checkin[0])
				{
					if (id == 0)
					{
						FOR(i, 1, 1000) if (checkin[i])
						{
							endowed[i] += cur - max(checkin[i], checkin[0]);
							DEBUG("endowed[", id, "] = ", endowed[id]);
						}
					}
					else
					{
						if (checkin[id])
						{
							endowed[id] += cur - max(checkin[id], checkin[0]);
							DEBUG("endowed[", id, "] = ", endowed[id]);
						}
					}
				}
				checkin[id] = 0;
			}
		}
		WRITE(*max_element(allof(endowed)));
	}
}

Measured memory_bytes: 1252