#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) REP(i,0,n)
#define REP(i,s,e) for(int i=(s); i<(int)(e); i++)
#define repr(i, n) REPR(i, n, 0)
#define REPR(i, s, e) for(int i=(int)(s-1); i>=(int)(e); i--)
#define pb push_back
#define all(r) r.begin(),r.end()
#define rall(r) r.rbegin(),r.rend()
#define fi first
#define se second

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const ll INF = 1e18;
const ll MOD = 1e9 + 7;
const double EPS = 1e-8;

template<typename T> T chmax(T& a, const T& b){return a = (a > b ? a : b);}
template<typename T> T chmin(T& a, const T& b){return a = (a < b ? a : b);}

struct UF{ //O(loga(n))
    int n;
    int m;
    vi d, r;
    UF(int n) : n(n), m(n), d(n, -1), r(n, 0){};
    int root(int i){
        if(d[i] < 0) return i;
        return d[i] = root(d[i]);
    }
    bool same(int x, int y){
        return root(x) == root(y);
    }
    bool unite(int x, int y){
        x = root(x);
        y = root(y);
        if(x == y) return false;

        if(r[x] < r[y]) swap(x, y);
        else if(r[x] == r[y]) r[x]++;
        d[x] += d[y];
        d[y] = x;
        --m;
        return true;
    }
    int size(int i){
        return -d[root(i)];
    }
    int size() {
        return m;
    }
};

int main(){
    int l, r;
    cin >> l >> r;
    ++r;
    UF uf(r);
    vector<int> a(r, 1);
    rep(i, l) a[i] = 0;
    REP(i, l, r) if(a[i]) {
        for(int j = i+i; j< r; j+=i) {
            a[j] = 0;
            uf.unite(i, j);
        }
    }
    cout << uf.size() - l  - 1<< '\n';
    return 0;
}