Conversion from int to std::shared_ptr

#include <memory>

void f1(std::shared_ptr<bool> ptr) {}

int main() {
    f1(0); // OK
    f1(1); // compilation error: could not convert ‘1’ from ‘int’ to ‘std::shared_ptr<bool>’
}

Both as int, why 0 but 1 can be converted to std::shared_ptr<T>?

How the disability of conversion from 1 to std::shared_ptr<T> be checked when compiling?