/* file : timetables.c */
/* author : Oscar Miró (o.miro.i.lopez.feliu@student.rug.nl) */
 
/* Description:
 * Receives input n, then n lines of inputs. Each of these receiving 3 ints each.
 * Forms a matrix with these, then finds if its possible to select a different number
 * from each row, then outputs how many rows could have their first column chosen.
 */

#include <stdio.h>

int rec (int size, int assigned[size], int input[size][3], int position, int count, int arr[]) {

    // checks if on end of the branch
    if (position == size) {
        // returns 1 and stores count to the pointer
        if (arr[0] < count) arr[0] = count;
        return 1;
    }

    // iterates 3 times, for every number in input. If unselected, branches out and selects
    int n = 0;
    for (int i = 0; i < 3; i++) {
        if (assigned[input[position][i]] == 0) {

            if (i == 0) count++;
            assigned[input[position][i]]++;
            n+= rec(size, assigned, input, position + 1, count, arr);
            if (i == 0) count--;
            assigned[input[position][i]]--;
        } 
    }
    return n;
}

int main (int argc, char *argv[]) {

    // declaration and assigning
    int size;
    scanf("%d", &size);

    int input[size][3], assigned[size], arr[1] = {0};

    // initializes array and scans
    for (int i = 0; i < size; i++) {
        assigned[i] = 0;
        scanf("%d %d %d", &input[i][0], &input[i][1], &input[i][2]);
    }
    
    // prints appropiate output
    int max = rec(size, assigned, input, 0, 0, arr);
    if (max) {
        printf("%d\n", arr[0]);
    } else {
        printf("IMPOSSIBLE\n");
    }
}