View Compilation Error

0_0_17166937_30397.cpp: In function 'int main()':
0_0_17166937_30397.cpp:25:31: error: 'k' was not declared in this scope
         mn = min(i * x + (n % k) * f[n / k + 1] + (k - n % k) * f[n / k], mn);
                               ^