View Compilation Error

0_0_29298195_7380.cpp: In function 'int main()':
0_0_29298195_7380.cpp:36:49: error: invalid operands of types 'int' and '<unresolved overloaded function type>' to binary 'operator<<'
         printf("%d\n", solve(k) - solve(0))  << endl;
                                                 ^