View Compilation Error

0_0_2940380_3430.cpp: In function `long long int phi(long long int)':
0_0_2940380_3430.cpp:12: error: `sqrt' undeclared (first use this function)
0_0_2940380_3430.cpp:12: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_2940380_3430.cpp: In function `long long int calc(long long int, long long int, int)':
0_0_2940380_3430.cpp:57: error: `k' undeclared (first use this function)
0_0_2940380_3430.cpp: In function `int main()':
0_0_2940380_3430.cpp:75: error: expected unqualified-id before "int"
0_0_2940380_3430.cpp:75: error: expected `,' or `;' before "int"
0_0_2940380_3430.cpp:77: error: `c' undeclared (first use this function)