Matrix Diagonal Sum

class Solution {
public:
    int diagonalSum(vector<vector<int>>& mat) {
        int sum=0;
        for(int i=0;i<mat.size();i++)
        {
            for(int j=0;j<mat[i].size();j++)
            {
                if(i==j)
                {
                    sum+=mat[i][j];
                }
            }
        }
        int i=0;
        int j=mat.size()-1;
        while(i<mat.size())
        {
            sum+=mat[i][j];
            i++;
            j--;
        }
        if(mat.size()%2!=0)
        {
            int k=mat.size();
            sum-=mat[k/2][k/2];
        }
        return sum;

    }
};