#include <iostream>
#include <sstream>


using namespace std;

int main() {

	string isbn_before, sec_co, thi_co, fou_co, sec_st, thi_st;
	int fir = 0, sec = 0, thi = 0, fou = 0;
	int sec_cop, thi_cop;
	cin >> isbn_before;

	stringstream convert;
	for (int i = 2; i <= 4; ++i) {
		sec_co = isbn_before[i];
		convert << sec_co;
		convert >> sec_cop;
		sec += i * sec_cop;
	}

	return 0;
}

程序还没写完，想着运行试一下结果提示“连接器返回错误代码”，请问这样一般是哪里出错了？qwq