#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int min(int a, int b) {
    return a < b ? a : b;
}

int solution(int batchSize, int* groups, int n) {
    // Count frequency of each remainder
    int* remainders = (int*)calloc(batchSize, sizeof(int));
    for (int i = 0; i < n; i++) {
        remainders[groups[i] % batchSize]++;
    }
    
    // Groups with remainder 0 are always happy
    int happy = remainders[0];
    
    // Count non-zero remainder groups
    int nonZeroSum = 0;
    for (int i = 1; i < batchSize; i++) {
        nonZeroSum += remainders[i];
    }
    
    // If no other groups, return count of remainder-0 groups
    if (nonZeroSum == 0) {
        free(remainders);
        return happy;
    }
    
    // First group (if any non-zero remainder groups exist) is always happy
    if (nonZeroSum > 0) {
        happy += 1;
    }
    
    // Pair complementary remainders optimally
    for (int i = 1; i <= batchSize / 2; i++) {
        int complement = batchSize - i;
        if (i == complement) {
            // Can pair these among themselves, each pair contributes 1 happy group
            happy += (remainders[i] - 1) / 2;
        } else if (i < complement) {
            // Pair i with complement, each pair contributes 1 happy group
            happy += min(remainders[i], remainders[complement]);
        }
    }
    
    free(remainders);
    return happy;
}

int main() {
    int batchSize;
    scanf("%d", &batchSize);
    
    char line[1000];
    fgets(line, sizeof(line), stdin);
    fgets(line, sizeof(line), stdin);
    
    int groups[30];
    int n = 0;
    char* token = strtok(line + 1, ",]");
    while (token != NULL) {
        groups[n++] = atoi(token);
        token = strtok(NULL, ",]");
    }
    
    printf("%d\n", solution(batchSize, groups, n));
    return 0;
}