数学 Codeforces Round #308 (Div. 2) B. Vanya and Books

题目传送门

 /*
     水题：求总数字个数，开long long竟然莫名其妙WA了几次，也没改啥又对了:)
 */
 #include <cstdio>
 #include <iostream>
 #include <algorithm>
 #include <cstring>
 #include <cmath>
 #include <vector>
 #include <string>
 #include <queue>
 #include <map>
 #include <set>
 using namespace std;

 typedef long long ll;
 const int MAXN = 1e2 + ;
 const int INF = 0x3f3f3f3f;

 int main(void)      //Codeforces Round #308 (Div. 2) B. Vanya and Books
 {
     // freopen ("B.in", "r", stdin);

     ll n;
     while (scanf ("%I64d", &n) == )
     {
         int len = ;    ll tmp = n;
         while (tmp)
         {
             tmp /= ;    len++;
         }

         ll ans = ;    ll x = ;
         for (int i=; i<=len-; ++i)
         {
             ans += x * i;    x *= ;
         }
         ll y = ;
         for (int i=; i<=len-; ++i)    y *= ;

         ans += (n - y + ) * len;
         printf ("%I64d\n", ans);
     }

     return ;
 }