#include <iostream>
using namespace std;
int main()
{
    long long num, sum = 0;
    cin >> num;
    long long *arr = new long long[num];
    for (long long i = 0; i < num; i++)
    {
        cin >> arr[i];
        sum += arr[i];
    }
    long long lsum = 0;
    for (long long i = 0; i < num - 1; i++)
    {
        lsum += arr[i];
        if (lsum == sum - lsum - arr[i+1])
        {
            cout << "i = " << i+1 << endl;
            return 0;
        }
    }
    cout << "It's impossible\n";
}
 

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