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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. #define ll unsigned long long
  5.  
  6. int main() {
  7. 	ll n;
  8. 	cin >> n;
  9.     ll x1 = n, cnt = 0;
  10. //    Считаем количество цифр
  11.     while (x1) x1 /= 10, cnt++;
  12.     int d[cnt], i = 1;
  13.     x1 = n;
  14. //    Заполняем массив цифр
  15.     while (x1) d[cnt - i++] = x1 % 10, x1 /= 10;
  16. //    Заменяем цифры после 8 на 799999...
  17.     bool f = false;
  18.     for (int i = 0; i < cnt; i++)
  19.         if (f)
  20.             d[i] = 9;
  21.         else if (d[i] == 8)
  22.             d[i] = 7, f = true;
  23. //    Считаем степени девятки
  24.     ll pow9[19];
  25.     pow9[0] = 1;
  26.     for (int i = 1; i <= 18; i++)
  27.         pow9[i] = pow9[i - 1] * 9;
  28. //    Считаем ответ
  29.     ll res = 0;
  30.     for (int i = cnt - 1; i >= 0; i--)
  31.         res += pow9[cnt - i - 1] * (d[i] - (d[i] >= 8));
  32.     cout << res <<endl;
  33. }
  34.  
Success #stdin #stdout 0s 15232KB
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stdin
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88888888888888
stdout
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20334926626631
https://ideone.com/SaYePo
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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