#include <stdio.h>

int main()
{
  char a[110], b[110], c[110];
  int n;
  
  scanf("%d%s%s%s", &n, a, b, c);
  int x = 0;
  for (int i = 0; i < n; ++i)
  {
    if (a[i] == b[i])
    {
      if (c[i] != a[i]) ++x;
    }
    else
    {
      if (c[i] == a[i] || c[i] == b[i]) ++x; else x += 2;
    }
  }
  printf("%d\n", x);
}