825 B | 825 chars
#include <bits/stdc++.h>
#define for1(s,n) for(int i = s; i < n; i++)
#define for1j(s,n) for(int j = s; j < n; j++)
#define foreach(k) for(auto i : k)
#define foreachj(k) for(auto j : k)
#define pb(a) push_back(a)
#define sz(a) a.size()
using namespace std;
typedef unsigned long long ull;
typedef long long ll;
typedef vector <int> iv1;
typedef vector <vector<int>> iv2;
typedef vector <ll> llv1;
typedef unsigned int uint;
typedef vector <ull> ullv1;
typedef vector <vector <ull>> ullv2;
ll N;
ll Z = 1;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> N;
for1(2, N+1) {
ll k = i;
while(k % 10 == 0) {
k/=10;
}
Z = Z * k;
while(Z%10 == 0) {
Z /=10;
}
Z %=100000000;
}
cout << Z % 10;
}