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  1. #include <iostream>
  2. #include <vector>
  3. #include <algorithm>
  4. using namespace std;
  5.  
  6.  
  7. unsigned long long iqpow(unsigned long long x,
  8.                          unsigned long long e,
  9.                          unsigned long long p)
  10. {
  11.     unsigned long long res = 1;
  12.     x %= p;
  13.     for(;e;e>>=1)
  14.     {
  15.         if (e&1) res = (res*x)%p;
  16.         x = (x*x)%p;
  17.     }
  18.     return res;
  19. }
  20.  
  21. int main()
  22. {
  23.     unsigned long long n, m, l, mod = 1000000007, ans = 0;
  24.     cin >> n >> m >> l;
  25.     vector <unsigned long long> fac(n + 2, 1);
  26.     for (int i = 2; i <= n + 1; ++ i){fac[i] = fac[i - 1] * i % mod;}
  27.  
  28.     for (int k = 1; k <= l && m*k <= n; ++k)
  29.     {
  30.         ans = (ans + (fac[n] * iqpow(fac[n - m * k] * fac[m * k] % mod, mod - 2, mod) % mod)) % mod;
  31.     }
  32.     cout << ans;
  33.     return 0;
  34. }
  35.  
Success #stdin #stdout 0.04s 11204KB
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936253510
https://ideone.com/9bu0DB
language:
C++14 (gcc 8.3)
created:
2 years ago
visibility:
secret

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