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gcc prog3.cpp 
/tmp/cc3ySQj4.o: In function `std::__verify_grouping(char const*, unsigned int, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
prog3.cpp:(.text+0xe): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::size() const'
prog3.cpp:(.text+0x59): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::operator[](unsigned int) const'
prog3.cpp:(.text+0x97): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::operator[](unsigned int) const'
prog3.cpp:(.text+0xdf): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::operator[](unsigned int) const'
/tmp/cc3ySQj4.o: In function `__static_initialization_and_destruction_0(int, int)':
prog3.cpp:(.text+0x129): undefined reference to `std::ios_base::Init::Init()'
/tmp/cc3ySQj4.o: In function `__tcf_0':
prog3.cpp:(.text+0x176): undefined reference to `std::ios_base::Init::~Init()'
/tmp/cc3ySQj4.o: In function `main':
prog3.cpp:(.text+0x19b): undefined reference to `std::cout'
prog3.cpp:(.text+0x1a0): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
prog3.cpp:(.text+0x1a8): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)'
prog3.cpp:(.text+0x1b0): undefined reference to `std::basic_ostream<char, std::char_traits<char> >::operator<<(std::basic_ostream<char, std::char_traits<char> >& (*)(std::basic_ostream<char, std::char_traits<char> >&))'
prog3.cpp:(.text+0x1be): undefined reference to `std::cin'
prog3.cpp:(.text+0x1c3): undefined reference to `std::basic_istream<char, std::char_traits<char> >::operator>>(int&)'
prog3.cpp:(.text+0x1e3): undefined reference to `std::cout'
prog3.cpp:(.text+0x1e8): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
prog3.cpp:(.text+0x1f0): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)'
prog3.cpp:(.text+0x1f8): undefined reference to `std::basic_ostream<char, std::char_traits<char> >::operator<<(std::basic_ostream<char, std::char_traits<char> >& (*)(std::basic_ostream<char, std::char_traits<char> >&))'
prog3.cpp:(.text+0x213): undefined reference to `std::cout'
prog3.cpp:(.text+0x218): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
prog3.cpp:(.text+0x220): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)'
prog3.cpp:(.text+0x228): undefined reference to `std::basic_ostream<char, std::char_traits<char> >::operator<<(std::basic_ostream<char, std::char_traits<char> >& (*)(std::basic_ostream<char, std::char_traits<char> >&))'
prog3.cpp:(.text+0x24b): undefined reference to `std::cin'
prog3.cpp:(.text+0x250): undefined reference to `std::basic_istream<char, std::char_traits<char> >::operator>>(int&)'
/tmp/cc3ySQj4.o:(.eh_frame+0x11): undefined reference to `__gxx_personality_v0'
collect2: ld returned 1 exit statu