// Problem: P1303 A*B Problem
// Contest: Luogu
// URL: https://www.luogu.com.cn/problem/P1303
// Memory Limit: 125 MB
// Time Limit: 1000 ms
// User: Pannnn
#include
using namespace std;
// 高精度加法
vector sum(vector a, vector b) {
vector res;
int p = 0;
for (int i = 0; i < a.size() || i < b.size(); ++i) {
if (i < a.size()) {
p += a[i];
}
if (i < b.size()) {
p += b[i];
}
res.push_back(p % 10);
p /= 10;
}
if (p) {
res.push_back(p);
}
return res;
}
// vector与单个数字的乘法,由于有前移,所以将res以引用传递
void mul(vector a, int b, vector &res) {
int p = 0;
for (int i = 0; i < a.size() || p != 0; ++i) {
if (i < a.size()) {
p += a[i] * b;
}
res.push_back(p % 10);
p /= 10;
}
}
vector mul(vector a, vector b) {
vector res;
for (int i = 0; i < b.size(); ++i) {
// 模拟乘法运算,b的每一位与a相乘,移位后累加到结果中
// 提前在临时结果vector中添加i个0,以引用传递进去
vector tRes(i);
mul(a, b[i], tRes);
res = sum(tRes, res);
}
// 去除结果中不必要的前导0
while (res.size() > 1 && res.back() == 0) {
res.pop_back();
}
return res;
}
vector reverse(string num) {
vector res;
for (int i = num.length() - 1; i >= 0; --i) {
res.push_back(num[i] - '0');
}
return res;
}
int main() {
string a, b;
cin >> a >> b;
vector num1 = reverse(a);
vector num2 = reverse(b);
vector res = mul(num1, num2);
for (int i = res.size() - 1; i >= 0; --i) {
cout << res[i];
}
cout << endl;
return 0;
}