Loop through each cell in grid and check it's neighbors

```
public int IslandPerimeter(int[,] grid) {
int perimeter = 0;
for(int i=0;i<grid.GetLength(0);i++)
{
for(int j=0;j<grid.GetLength(1);j++)
{
if(grid[i,j] == 1)
{
if(j == 0 || grid[i,j-1] != 1) perimeter++;
if(j == grid.GetLength(1) -1 || grid[i, j+1] != 1 ) perimeter++;
if(i == 0 || grid[i-1, j] != 1) perimeter++;
if(i == grid.GetLength(0) -1 || grid[i+1, j] != 1) perimeter++;
}
}
}
return perimeter;
}
```