View Compilation Error

0_0_2603627_26160.cpp: In function `long long int solve(long long int, long long int)':
0_0_2603627_26160.cpp:93: error: `sqrt' undeclared (first use this function)
0_0_2603627_26160.cpp:93: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_2603627_26160.cpp: In function `int main()':
0_0_2603627_26160.cpp:125: error: `sqrt' undeclared (first use this function)