View Compilation Error

0_0_6006306_11156.cpp: In function `int main()':
0_0_6006306_11156.cpp:7: error: `F' undeclared (first use this function)
0_0_6006306_11156.cpp:7: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_6006306_11156.cpp: In function `int F(int)':
0_0_6006306_11156.cpp:15: error: `int F(int)' used prior to declaration