#if __has_include("../library/Basic/Debug.hpp")

#include "../library/Basic/Debug.hpp"

#else

/* ----- Header Files ----- */
// IO
#include <cstdio>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm
#include <algorithm>
#include <cmath>
#include <numeric>

// container
#include <vector>
#include <string>
#include <tuple>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>

// others
#include <random>
#include <limits>
#include <functional>
#include <ctime>
#include <cassert>
#include <cstdint>


/* ----- Type Alias ----- */
using Int = long long int;
using Real = long double;
using String = std::string;
template <class... Ts>
using Tuple = std::tuple<Ts...>;

template <class T>
using Vector = std::vector<T>;
template <class T>
using Queue = std::queue<T>;
template <class T>
using Stack = std::stack<T>;
template <class T>
using Deque = std::deque<T>;

template <class T>
using MaxHeap = std::priority_queue<T>;
template <class T>
using MinHeap = std::priority_queue<T, std::vector<T>, std::greater<T>>;
template <class T>
using Set = std::set<T>;
template <class T, class U>
using Map = std::map<T, U>;

template <class T, class... Us>
using Func = std::function<T(Us...)>;

template <class T>
T genv(T v) { return v; }

template <class T, class... Ts>
auto genv(size_t l, Ts... ts) {
    return Vector<decltype(genv<T>(ts...))>(l, Vector<T>(ts...));
}

template <class Cost = Int>
struct Edge {
    Int src, dst;
    Cost cost;
    Edge(Int src = -1, Int dst = -1, Cost cost = 1)
        : src(src), dst(dst), cost(cost){};

    bool operator<(const Edge<Cost>& e) const { return this->cost < e.cost; }
    bool operator>(const Edge<Cost>& e) const { return this->cost > e.cost; }
};

template <class Cost = Int>
using Edges = Vector<Edge<Cost>>;
template <class Cost = Int>
using Graph = Vector<Vector<Edge<Cost>>>;

#endif

/* ----- Misc ----- */
void fastio() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
}

struct Fout {
    Int precision;
    Fout(Int precision) : precision(precision) {}
};
std::ostream& operator<<(std::ostream& os, const Fout& fio) {
    os << std::fixed << std::setprecision(fio.precision);
    return os;
}


/* ----- Constants ----- */
// constexpr Int INF = std::numeric_limits<Int>::max() / 3;
// constexpr Int MOD = 1000000007;
// constexpr Real PI = acos(-1);
// constexpr Real EPS = 1e-10;
// std::mt19937 mt(int(std::time(nullptr)));

bool solve() {
    Int n;
    std::cin >> n;
    if (n == 0) return false;

    Vector<Vector<Int>> records(1000);
    for (Int i = 0; i < n; ++i) {
        Int t, id;
        {
            Int m, d, h, mi;
            char c;
            std::cin >> m >> c >> d >> h >> c >> mi >> c >> id;
            t = ((m * 40 + d) * 24 + h) * 60 + mi;
        }
        records[id].push_back(t);
    }

    Vector<Vector<Tuple<Int, Int>>> segs(1000);
    for (Int i = 0; i < 1000; ++i) {
        for (Int j = 0; j < records[i].size(); j += 2) {
            segs[i].emplace_back(records[i][j], records[i][j + 1]);
        }
    }

    Int ans = -1;
    for (Int i = 1; i < 1000; ++i) {
        Int t = 0;
        for (auto p : segs[i]) {
            for (auto g : segs[0]) {
                Int lp, rp, lg, rg;
                std::tie(lp, rp) = p, std::tie(lg, rg) = g;
                Int l = std::max(lp, lg), r = std::min(rp, rg);
                t += std::max(0LL, r - l);
            }
        }
        ans = std::max(ans, t);
    }

    std::cout << ans << std::endl;
    return true;
}

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



Measured memory_bytes: 3204