#include<bits/stdc++.h>

#define isz(x) int(x.size())
#define all(x) x.begin(),x.end()
#define ll long long
#define pii pair<int,int>
#define fi first
#define se second
#define isz(x) int(x.size())
#define ull unsigned long long
#define vi vector<int>
#define vll vector<ll>
#define vch vector<char>
#define vvch vector<vch>
#define vvi vector<vector<int>>
#define vvvi vector<vvi>
#define vvll vector<vector<ll>>
#define vpii vector<pair<int,int>>
#define vvpii vector<vpii>
#define forn(i,n) for(int i=0;i<(int)n;++i)
#define pb push_back

using namespace std;

const int UNDEF = -1;
const int MOD = 1e9 + 7;
const int INF = 1e9;

ll solve(ll R,vll& p){
    int N=isz(p);

    ll ans=0;
    for(int mask=1;mask<(1<<N);++mask){
        ll bits=0,mult=1;
        for(int j=0;j<N;++j){
            if(mask&(1<<j)){
                if(1.0L*mult*p[j]>R){
                   mult=R+1;
                   break;
                }
                mult*=p[j];
                bits++;
            }
        }
        if(bits&1) ans+=R/mult;
        else ans-=R/mult;
    }

    return ans;
}


int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    //freopen("input.txt", "rt", stdin);
    //freopen("output.txt", "wt", stdout);

    ll L,R,N;
    cin>>L>>R>>N;

    vll p(N);
    forn(i,N) cin>>p[i];
    p.erase(unique(all(p)),p.end());

    cout<<solve(R,p)-solve(L-1,p);

    return 0;
}