uva 10212 - The Last Non-zero Digit.

 1 #include <cstdio>
 2 #define ll long long
 3 
 4 const ll MOD = 1e9;
 5 
 6 int main()
 7 {
 8     ll N, M;
 9     while(scanf("%lld%lld", &N, &M) != EOF)
10     {
11         ll ans = 1;
12         while(M--)
13         {
14             ans *= N--;
15             while(! (ans % 10)) ans /= 10;
16             ans %= MOD;
17         }
18         printf("%lld\n", ans % 10);
19     }
20     return 0;
21 }