#include 

using namespace std;

int main()
{
    int a, b;
    int zbir = 0;
    cin >> a;
    cin >> b;
    for (int i = a; i <= b; i += 1)
    {
        if (i % 2 == 1)
        {
            zbir += i;
        }
    }
    cout << zbir << endl;
    return 0;
}