Find the time complexity of sum of two matrices

What is the time complexity of the program for the sum of two matrices?

Step count method

void sum()

{

int n, a[n][n],b[n][n],c[n][n],i,j; //----0 

for(i=0;i<n;i++) //----n+1

  { 

    for(j=0;j<n;j++) //----n+1

      {

        c[i][j]=a[i][j]+b[i][j]; //----n 

      }

  }

}

f(n) = 0 + (n+1) * (n+1+n)

f(n) = (n+1)*(2n+1)

f(n) =  2n² + 3n + 1

f(n) = O(n²)