#include <iostream>
#include <memory.h>
#include <map>
#include <string>
#include <functional>
#include <vector>
using namespace std;
typedef long long ll;
ll n, k;
ll fa(ll a)
{
if (a == 0)
return 1;
ll res = 1;
for (int i = 1; i <= a; i++)
res *= i;
return res;
}
ll po(ll a)
{
if (k == 0)
return 1;
ll res = 1;
for (int i = 0; i < k; i++)
res = res * a;
return res;
}
int main() {
ios::sync_with_stdio(false);
cin >> n >> k;
ll res = 0;
for (ll i = 0; i <= n; i++)
{
res = res + (po(fa(i)));
}
while (1)
{
if (res == 0)
return 0;
else if (res % 10 != 0) {
cout << res % 10 << endl;
return 0;
}
res = res / 10;
}
return 0;
}
