a times b

/usr/bin/ld: output/ccxDsekV.o: in function `main.cold':
code.cpp:(.text.unlikely+0x7): undefined reference to `__gmpz_clear'
/usr/bin/ld: code.cpp:(.text.unlikely+0xf): undefined reference to `__gmpz_clear'
/usr/bin/ld: code.cpp:(.text.unlikely+0x17): undefined reference to `__gmpz_clear'
/usr/bin/ld: output/ccxDsekV.o: in function `main':
code.cpp:(.text.startup+0x2a): undefined reference to `__gmpz_init'
/usr/bin/ld: code.cpp:(.text.startup+0x32): undefined reference to `__gmpz_init'
/usr/bin/ld: code.cpp:(.text.startup+0x41): undefined reference to `operator>>(std::istream&, __mpz_struct*)'
/usr/bin/ld: code.cpp:(.text.startup+0x4c): undefined reference to `operator>>(std::istream&, __mpz_struct*)'
/usr/bin/ld: code.cpp:(.text.startup+0x59): undefined reference to `__gmpz_init'
/usr/bin/ld: code.cpp:(.text.startup+0x67): undefined reference to `__gmpz_mul'
/usr/bin/ld: code.cpp:(.text.startup+0x76): undefined reference to `operator<<(std::ostream&, __mpz_struct const*)'
/usr/bin/ld...

#include <bits/stdc++.h>
#include <gmpxx.h>
using namespace std;

int main() {
    mpz_class a, b;
    cin >> a >> b;
    cout << a * b;
}