#include <stdio.h>
int main() {
    int N, M;
    scanf("%d", &N);
    scanf("%d", &M);
    int hashTable[N];
    for (int i = 0; i < N; i++) {
        hashTable[i] = -1;
    }
    for (int i = 0; i < M; i++) {
        int key;
        scanf("%d", &key);
        int idx = key % N;
        while (hashTable[idx] != -1) {
            idx = (idx + 1) % N;
        }
        hashTable[idx] = key;
    }
    int clusters = 0;
    int inCluster = 0;
    for (int i = 0; i < N; i++) {
        if (hashTable[i] != -1) {
            if (!inCluster) {
                clusters++;
                inCluster = 1;
            }
        } else {
            inCluster = 0;
        }
    }
    printf("%d\n", clusters);
    return 0;
}