注意使用long long

#include<iostream>
using namespace std;
int main()
{
	int a, n;
	cin >> a >> n;
	long long ans = 0, num = a;
	for (int i = 1; i <= n; i++) {
		ans += num;
		num *= 10;
		num += a;
	}
	cout << ans << endl;
	return 0;
}