Recently I started practicing coding on this website and I have a problem with code submission that there shows message "Line 57: redefinition of ‘int main()’." everytime I submit my solution.

I do not know why and the code itself works fine on my computer.

Here is the code

```
#include <vector>
```

#include <iostream>

using namespace std;

class Solution {

public:

vector<int> twoSum(vector<int>& nums, int target) {

vector<int> index_1_result, index_2_result;

int i, j, number_1, number_2, sum;

```
int length_input = nums.size();
// Find all the possible combination;
for (i = 0; i < length_input; i++){
number_1 = nums.at(i);
for (j = i + 1; j < length_input; j++){
number_2 = nums.at(j);
sum = number_1 + number_2;
if (sum == target){
cout << "number 1 = " << number_1 << "\n";
cout << "number 2 = " << number_2 << "\n";
index_1_result.push_back(i + 1);
index_2_result.push_back(j + 1);
}
}
}
vector<int> result_return;
// Since there is only a result by assumption;
result_return.push_back(index_1_result.at(0));
result_return.push_back(index_2_result.at(0));
return result_return;
}
```

};

int main(){

```
Solution solution1;
vector<int> nums, result;
nums.push_back(2);
nums.push_back(7);
nums.push_back(11);
nums.push_back(15);
int target = 9;
result = solution1.twoSum(nums, target);
cout << "index1 = " << result.at(0) << ", " << "index2 = " << result.at(1) << "\n";
return 0;
```

}