#include <functional>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <cstring>
#include <string>
#include <vector>
#include <random>
#include <bitset>
#include <queue>
#include <cmath>
#include <stack>
#include <set>
#include <map>
typedef long long ll;
using namespace std;
const ll MOD = 1000000007LL;

bool is_prime(int n) {
    for (int i = 2; i * i <= n; i++) {
        if (n % i == 0) return false;
    }
    return n != 1;
}

int main() {
    int l, r;
    cin >> l >> r;

    vector<int> primes;
    for (int i = l; i <= r; i++) {
        if (is_prime(i)) {
            primes.push_back(i);
        }
    }

    int sum = 0;
    for (int i = l + 1; i <= r; i++) {
        int mn = 1;
        for (int x : primes) {
            if (x >= i) break;
            mn = min(mn, i % x);
        }
        sum += mn;
    }

    cout << sum << endl;
    return 0;
}