class Solution {
public:
    string multiply(string num1, string num2) {
        long long ans=0, x;
        int i, j;
        int num1_sz = num1.size()-1, num2_sz = num2.size()-1;
        
        for (i=num1_sz; i>-1; i--) {
            x = pow(10, num1_sz-i)*(num1[i]-'0');
            for (j=num2_sz; j>-1; j--) {
                ans += x*pow(10, num2_sz-j)*(num2[j]-'0');
            }
        }
        return to_string(ans);
    }
};