/**
* 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;
}