#pragma GCC optimize ("O3")
#pragma GCC target ("avx")
#include "bits/stdc++.h" // define macro "/D__MAI"

using namespace std;
typedef long long int ll;

#define xprintf(fmt,...) fprintf(stderr,fmt,__VA_ARGS__)
#define debugv(v) {printf("L%d %s > ",__LINE__,#v);for(auto e:v){cout<<e<<" ";}cout<<endl;}
#define debuga(m,w) {printf("L%d %s > ",__LINE__,#m);for(int x=0;x<(w);x++){cout<<(m)[x]<<" ";}cout<<endl;}
#define debugaa(m,h,w) {printf("L%d %s >\n",__LINE__,#m);for(int y=0;y<(h);y++){for(int x=0;x<(w);x++){cout<<(m)[y][x]<<" ";}cout<<endl;}}
#define ALL(v) (v).begin(),(v).end()
#define repeat(cnt,l) for(auto cnt=0ll;(cnt)<(l);++(cnt))
#define iterate(cnt,b,e) for(auto cnt=(b);(cnt)!=(e);++(cnt))
#define MD 1000000007ll
#define PI 3.1415926535897932384626433832795
#define EPS 1e-12
template<typename T1, typename T2> ostream& operator <<(ostream &o, const pair<T1, T2> p) { o << "(" << p.first << ":" << p.second << ")"; return o; }
template<typename iterator> inline size_t argmin(iterator begin, iterator end) { return distance(begin, min_element(begin, end)); }
template<typename iterator> inline size_t argmax(iterator begin, iterator end) { return distance(begin, max_element(begin, end)); }
template<typename T> T& maxset(T& to, const T& val) { return to = max(to, val); }
template<typename T> T& minset(T& to, const T& val) { return to = min(to, val); }

mt19937_64 randdev(8901016);
inline ll rand_range(ll l, ll h) {
    return uniform_int_distribution<ll>(l, h)(randdev);
}

#ifdef __MAI
#define getchar_unlocked getchar
#define putchar_unlocked putchar
#endif
#ifdef __VSCC
#define getchar_unlocked _getchar_nolock
#define putchar_unlocked _putchar_nolock
#endif
namespace {
#define isvisiblechar(c) (0x21<=(c)&&(c)<=0x7E)
    class MaiScanner {
    public:
        template<typename T> void input_integer(T& var) {
            var = 0;
            T sign = 1;
            int cc = getchar_unlocked();
            for (; cc<'0' || '9'<cc; cc = getchar_unlocked())
                if (cc == '-') sign = -1;
            for (; '0' <= cc&&cc <= '9'; cc = getchar_unlocked())
                var = (var << 3) + (var << 1) + cc - '0';
            var = var*sign;
        }
        inline int c() { return getchar_unlocked(); }
        inline MaiScanner& operator>>(int& var) {
            input_integer<int>(var);
            return *this;
        }
        inline MaiScanner& operator>>(long long& var) {
            input_integer<long long>(var);
            return *this;
        }
        inline MaiScanner& operator>>(string& var) {
            int cc = getchar_unlocked();
            for (; !isvisiblechar(cc); cc = getchar_unlocked());
            for (; isvisiblechar(cc); cc = getchar_unlocked())
                var.push_back(cc);
            return *this;
        }
        template<typename IT> void in(IT begin, IT end) {
            for (auto it = begin; it != end; ++it) *this >> *it;
        }
    };
}
MaiScanner scanner;



template<typename T = ll>
class bitree {
public:
    int size;
    vector<T> data;
    bitree(int size) :size(size + 1), data(size + 1) {}

    // -------------------------------------------------------
    // 和に関するBIT
    // 1..rの範囲の値の和を求める．
    T sum(int r) {
        T s = 0;
        while (r) {
            s += data[r];
            r -= r&-r; //  r&-r と書くことで最下のビットを得る
        }
        return s;
    }
    // idxの要素の値をval増やす
    void add(int idx, T val) {
        while (idx <= size) {
            data[idx] += val;
            idx += idx&-idx;
        }
    }
};


template<typename INTEGER>
INTEGER b_search(INTEGER l, INTEGER h, auto func) {
    ++h;
    // --l;
    INTEGER c;
    while (l + 1 < h) {
        c = (l + h) / 2;
        if (func(c)) {
            h = c;
        }
        else {
            l = c;
        }
    }
    return h;
    // return l;
}


ll m, n, kei;

vector<pair<int, int>> sche;

int main() {
    scanner >> kei >> n;

    if (n <= kei) {
        cout << n << endl;
        return 0;
    }

    sche.reserve(n);

    repeat(i, n) {
        int a1, a2, a3, b1, b2, b3;
        scanf("%d %d:%d %d %d:%d", &a1, &a2, &a3, &b1, &b2, &b3);
        sche.emplace_back(b1 * 1440 + b2 * 60 + b3, a1 * 1440 + a2 * 60 + a3);
    }

    sort(ALL(sche));

    const int rangend = 1440 * 10;

    bitree<int> bit(rangend);

    int ans = 0;
    int cnt;
    for(auto s : sche) {
        if (0 < (cnt = bit.sum(s.second+1))) {
            int x = b_search(1, s.second, [&](int x) {return bit.sum(x) == cnt; });
            if (x < s.second) {
                bit.add(x, -1);
                bit.add(s.first, 1);
                ++ans;
            }
        }
        else if (bit.sum(rangend) < kei)
            bit.add(s.first, 1),
            ++ans;
    }

    cout << ans << endl;



    return 0;
}