#include <stdio.h>
#include <string.h>
#define N 100000
int min(int a, int b) { return a < b ? a : b; }
int max(int a, int b) { return a > b ? a : b; }
unsigned int X = 12345;
int rand_() {
return (X *= 3) >> 1;
}
int xx[N * 2];
void sort(int *ii, int l, int r) {
while (l < r) {
int i = l, j = l, k = r, i_ = ii[l + rand_() % (r - l)], tmp;
while (j < k) {
if (xx[ii[j]] == xx[i_])
j++;
else if (xx[ii[j]] < xx[i_]) {
tmp = ii[i], ii[i] = ii[j], ii[j] = tmp;
i++, j++;
} else {
k--;
tmp = ii[j], ii[j] = ii[k], ii[k] = tmp;
}
}
sort(ii, l, i);
l = k;
}
}
int iq[N + 1], pq[N], cnt;
int lt(int i, int j) { return xx[i << 1 | 1] > xx[j << 1 | 1]; }
int p2(int p) {
return (p *= 2) > cnt ? 0 : (p < cnt && lt(iq[p + 1], iq[p]) ? p + 1 : p);
}
void pq_up(int i) {
int p, q, j;
for (p = pq[i]; (q = p / 2) && lt(i, j = iq[q]); p = q)
iq[pq[j] = p] = j;
iq[pq[i] = p] = i;
}
void pq_dn(int i) {
int p, q, j;
for (p = pq[i]; (q = p2(p)) && lt(j = iq[q], i); p = q)
iq[pq[j] = p] = j;
iq[pq[i] = p] = i;
}
void pq_add(int i) {
iq[pq[i] = ++cnt] = i, pq_up(i);
}
int pq_remove_first() {
int i = iq[1], j = iq[cnt--];
if (j != i)
pq[j] = 1, pq_dn(j);
pq[i] = 0;
return i;
}
void pq_remove(int i) {
int j = iq[cnt--];
if (j != i)
pq[j] = pq[i], pq_up(j), pq_dn(j);
pq[i] = 0;
}
int main() {
static int cc[N], ii[N * 2];
int n, m, h, h_, h1, i, a, tmp, d, k, k_;
scanf("%d%d", &m, &n);
for (i = 0; i < n; i++) {
scanf("%d%d%d", &xx[i << 1 | 0], &xx[i << 1 | 1], &cc[i]), xx[i << 1 | 0]--, xx[i << 1 | 1]--;
if (xx[i << 1 | 0] > xx[i << 1 | 1])
tmp = xx[i << 1 | 0], xx[i << 1 | 0] = xx[i << 1 | 1], xx[i << 1 | 1] = tmp;
}
k_ = n + 1;
for (a = 0; a < m; a++) {
for (i = 0; i < n; i++) {
xx[i << 1 | 0]--, xx[i << 1 | 1]--;
if (xx[i << 1 | 0] < 0)
tmp = m + xx[i << 1 | 0], xx[i << 1 | 0] = xx[i << 1 | 1], xx[i << 1 | 1] = tmp;
}
for (i = 0; i < n * 2; i++)
ii[i] = i;
sort(ii, 0, n * 2);
memset(iq, 0, n * sizeof *iq), cnt = 0;
d = 0, k = 0;
for (h = 0; h < n * 2; h = h_) {
h_ = h + 1;
while (h_ < n * 2 && xx[ii[h_]] == xx[ii[h]])
h_++;
for (h1 = h; h1 < h_; h1++) {
i = ii[h1];
if ((i & 1) == 0)
pq_add(i >> 1), d++;
else {
if (iq[i >> 1])
pq_remove(i >> 1);
d--;
}
}
while (cnt > d / 2)
pq_remove_first(), k++;
}
k_ = min(k_, k);
}
printf("%d\n", k_);
return 0;
}
