#include <bits/stdc++.h>
using namespace std;
int main() {
    long long int a, b;
    cin >> a >> b;
    long long int first = (a % 2 == 0) ? a : a + 1;
    long long int last = (b % 2 == 0) ? b : b - 1;
    long long int count = (last - first) / 2 + 1;
    if (first > last) count = 0;
    cout << count;
    return 0;
}