uva 10212 - The Last Non-zero Digit.

 #include <cstdio>
 #define ll long long

 const ll MOD = 1e9;

 int main()
 {
     ll N, M;
     while(scanf("%lld%lld", &N, &M) != EOF)
     {
         ll ans = ;
         while(M--)
         {
             ans *= N--;
             while(! (ans % )) ans /= ;
             ans %= MOD;
         }
         printf("%lld\n", ans % );
     }
     return ;
 }