/**
 * Author: Sergey Kopeliovich (Burunduk30@gmail.com)
 * Date: 2015.01.03
 */

#include <bits/stdc++.h>

using namespace std;

#define forn(i, n) for (int i = 0; i < (int)(n); i++)

typedef long long ll;

const int N = 9;

ll sum = 0, a, b;
int n, p[N];

void go( int i, ll x, int sign ) {
  if (i == n) {
    sum += sign * (b / x - (a - 1) / x);
    return;
  }
  go(i + 1, x, sign);
  if (p[i] <= b / x)
    go(i + 1, x * p[i], -sign);
}

int main() {
  #define NAME "prosto"
  assert(freopen(NAME ".in", "r", stdin));
  assert(freopen(NAME ".out", "w", stdout));

  cin >> a >> b >> n;
  forn(i, n)
    cin >> p[i];
  go(0, 1, 1);
  cout << sum << endl;
  return 0;
}