View Compilation Error

0_0_28688305_2504.cpp: In function 'int main()':
0_0_28688305_2504.cpp:17:52: error: 'powf' is not a member of 'std'
             n1 = n1 + (s1.at(s1.length()-i-1)-'a')*std::powf(26, i);
                                                    ^
0_0_28688305_2504.cpp:17:52: note: suggested alternative:
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/cmath:44:0,
                 from 0_0_28688305_2504.cpp:3:
GCC4.9.2/x86_64-w64-mingw32/include/math.h:738:22: note:   'powf'
   __CRT_INLINE float powf(float _X,float _Y) { return ((float)pow((double)_X,(double)_Y)); }
                      ^