week_2_7

#include <iostream>
#include <vector>

using namespace std;

long long fib_number(int n, int j) {
        vector<long long> f(n);
        f[0] = 1;
        f[1] = 1;
        for (int i = 2; i < j; i++) {
                f[i] = f[i-1] + f[i-2];
        }

        long long sum = 0;

        for (int i = n-1; i < j; i++) {
                sum += f[i];
        }

        return sum % 10;
}

int main() {
        int n, j;
        cin >> n >> j;
        cout << fib_number(n, j) << endl;
}