#include <iostream>
using namespace std;
int n, m, k;
int a[11];

int main() {
	cin >> n >> m >> k;
	for (int i = 0; i < k; i++)
		cin >> a[i];
	int sum = 0, cnt = 0;
	while (sum != n) {
	
		for (int i = 0; i < k; i++)
			if (sum == a[i]) {
				m++;
			}
		sum = sum + m;
		cnt++;
	}
	cout << cnt << endl;
	return 0;
}