#include <bits/stdc++.h>
using namespace std;
const int nmax = 1e7;
bool f[nmax + 1];
void snt()
{
    memset(f , true , sizeof(f));
    f[0] = f[1] = false;
    for (int i = 2; i <= sqrt(nmax); ++i)
    if (f[i]) for (int j = i * i; j <= nmax; j += i)
    f[j] = false;
}
int a, b, s = 0;
int main()
{
    snt();
    cin >> a >> b;
    for (int i = a; i <= b; ++i)
    {
        if (f[i]) s += i;
    }
    cout << s;
    return 0;
}

#include <bits/stdc++.h>
using namespace std;
int a, b, tong = 0;
void sang() 
{
    int ma[b - a + 1];
    for (int i = 2; i <= sqrt(b); i++) 
        for (int j = max(i * i, (a + i - 1) / i * i); j <= b; j += i) 
            ma[j - a] = 0;
    for (int i = max(2, a); i <= b; i++) 
        if (ma[i - a]) 
            tong += i;
    cout << tong ;
}

int main() 
{
    cin >> a >> b;
    sang();
    return 0;
}

$#khanhtaon$