#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

typedef pair<int, int> PII;

const int N = 110, M = 1010;

int n, m, f[N], g[N], ans;
PII a[M];

int main() {
    scanf("%d%d", &n, &m);
    for (int i = 1, d1, h1, m1, d2, h2, m2, v1, v2; i <= m; ++i) {
        scanf("%d %d:%d %d %d:%d", &d1, &h1, &m1, &d2, &h2, &m2);
        v1 = d1 * 24 * 60 + h1 * 60 + m1;
        v2 = d2 * 24 * 60 + h2 * 60 + m2;
        a[i] = { v1, v2 };
    }
    sort(a + 1, a + m + 1, [](PII p1, PII p2) {
        return p1.second < p2.second || (p1.second == p2.second && p1.first < p2.first);
    });

    ans = 0;
    for (int i = 1; i <= m; ++i) {
        int bg = a[i].first, ed = a[i].second;
        int chosen = -1;
        for (int j = 1; j <= n; ++j) {
            if (f[j] < bg) {
                if (chosen == -1 || f[j] > f[chosen]) {
                    chosen = j;
                }
            }
        }
        if (chosen != -1) {
            f[chosen] = ed;
            ++ans;
        }
    }
    printf("%d\n", ans);

    return 0;
}