#include <iostream>
#include <cstdlib>

using namespace std;

unsigned long long snaga(unsigned long long b) {
    unsigned long long csnaga = b;
    unsigned long long bsnaga = 1;
    while(csnaga != 2) {
        for(int i = 2; i < csnaga; i++) {
            if(csnaga % i != 0) {
                csnaga = i;
                bsnaga++;
                break;
            }
        }
    }
    return bsnaga;
}

int main () {
    unsigned long long a;
    unsigned long long b;
    cin >> a >> b;
    
    unsigned long long snagica = 0;
    
    for(unsigned long long i = a; i <= b; i++) {
        snagica += snaga(i);
    }
    
    cout << snagica << endl;
    
    return 0;
}