Find perimeter of shapes formed with 1s in binary matrix

using System;

// C# program to find perimeter of area 
// covered by 1 in 2D matrix consists  
// of 0's and 1's 
public class GFG
{

    public  const int R = 3;
    public const int C = 5;

    // Find the number of covered side  
    // for mat[i][j]. 
    public static int numofneighbour(int[][] mat, int i, int j)
    {

        int count = 0;

        // UP 
        if (i > 0 && mat[i - 1][j] == 1)
        {
            count++;
        }

        // LEFT 
        if (j > 0 && mat[i][j - 1] == 1)
        {
            count++;
        }

        // DOWN 
        if (i < R - 1 && mat[i + 1][j] == 1)
        {
            count++;
        }

        // RIGHT 
        if (j < C - 1 && mat[i][j + 1] == 1)
        {
            count++;
        }

        return count;
    }

    // Returns sum of perimeter of shapes 
    // formed with 1s 
    public static int findperimeter(int[][] mat)
    {

        int perimeter = 0;

        // Traversing the matrix and  
        // finding ones to calculate  
        // their contribution. 
        for (int i = 0; i < R; i++)
        {
            for (int j = 0; j < C; j++)
            {
                if (mat[i][j] == 1)
                {
                    perimeter += (4 - numofneighbour(mat, i, j));
                }
            }
        }

        return perimeter;
    }

    // Driver code 
    public static void Main(string[] args)
    {
        int[][] mat = new int[][]
        {
            new int[] {0, 1, 0, 0, 0},
            new int[] {1, 1, 1, 0, 0},
            new int[] {1, 0, 0, 0, 0}
        };

        Console.WriteLine(findperimeter(mat));
    }
}

// This code is contributed by Shrikant13