#include <stdio.h>

int main() {
    int N, M;
    scanf("%d", &N);
    scanf("%d", &M);

    int keys[M];
    for (int i = 0; i < M; i++) {
        scanf("%d", &keys[i]);
    }

    int hashTable[N];
    for (int i = 0; i < N; i++) {
        hashTable[i] = -1;  // initialize with -1 meaning empty slot
    }

    int totalProbes = 0;

    for (int i = 0; i < M; i++) {
        int key = keys[i];
        int pos = key % N;
        int offset = 1 + (key % (N - 1));
        
        int probes = 1; // count first probe
        while (hashTable[pos] != -1) {
            pos = (pos + offset) % N;
            probes++;
        }

        hashTable[pos] = key;
        totalProbes += probes;
    }

    printf("%d\n", totalProbes);

    return 0;
}