#include <bits/stdc++.h>
#include <iomanip>
using namespace std;
#define reps(i,s,n) for(int i = s; i < n; i++)
#define rep(i,n) reps(i,0,n)
#define Rreps(i,n,e) for(int i = n - 1; i >= e; --i)
#define Rrep(i,n) Rreps(i,n,0)
#define ALL(a) a.begin(), a.end()
#define fi first
#define se second
typedef long long ll;
typedef vector<ll> vec;
typedef vector<vec> mat;

ll N,M,H,W,Q,K,A,B;
string S;
const ll MOD = 998244353;
//const ll MOD = (1e+9) + 7;
typedef pair<ll, ll> P;
const ll INF = (1LL<<62);

int main() {
    class union_find{
            vector<long> parent, tree_size;
        public:
            union_find(unsigned long _n) : parent(_n), tree_size(_n, 1){
                for(unsigned long i = 0; i < _n; ++i)parent[i] = i;
            }
            ll find(ll x){
                while(parent[x] != x)x = parent[x] = parent[parent[x]];
                return x;
            }
            void merge(ll a, ll b){
                a = find(a);
                b = find(b);
    	    if(a==b) return;
                if(tree_size[a] < tree_size[b])swap(a, b);
                tree_size[a] += tree_size[b];
                parent[b] = a;
                return;
            }
    	bool same(ll a, ll b){
    	    a = find(a);
    	    b = find(b);
    	    return a == b;
    	}
        };
    //uf.mergeのように使う
    //ufはMAX_N+1でとるか、代入時に0-indexedにする
    ll L, R;
    cin>>L>>R;
    //vector<bool> rm(R + 1, false);
    union_find uf(R + 1);
    reps(i,L,R){
        for(ll j = i * 2; j <= R; j += i){
            uf.merge(i, j);
        }
    }
    ll ans = -1;
    reps(i,L, R + 1){
        if(!uf.same(i, 0)){
            ++ans;
            uf.merge(i, 0);
        }
    }
    cout<<ans<<endl;
}