#include <bits/stdc++.h>
using namespace std;

// types
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef pair<ld,ld> pdd;
typedef vector<ll> vll;

// macros
#define ALL(a) a.begin(),a.end()
#define SZ(a) ((int)a.size())
#define FI first
#define SE second
#define REP(i,n) for(int i=0;i<((int)n);i++)
#define REP1(i,n) for(int i=1;i<((int)n);i++)
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define PB push_back
#define EB emplace_back
#define MP(a,b) make_pair(a,b)
#define SORT_UNIQUE(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
#define GET_POS(c,x) (lower_bound(c.begin(),c.end(),x)-c.begin())
#define Decimal fixed<<setprecision(20)
#define INF 1000000000
#define LLINF 1000000000000000000LL

// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double eps = 1e-10;
const int MOD = 1e9 + 7;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};

int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  
  ll n;
  cin>>n;
  string a,b,c;
  cin>>a>>b>>c;
  
  ll ans=0;
  REP(i,n){  
    map<ll,ll> m;
    m[a[i]-'a']+=1;
    m[b[i]-'a']+=1;
    m[c[i]-'a']+=1;
    
    ll h=0;
    REP(j,26)
      h=max(h,m[j]);
    ans+=3-h;
    //cout<<n-h<<endl;
  }
  
  cout<<ans<<endl;
}
#include<bits/stdc++.h>
using namespace std;
namespace FAST_IO
{
	template<typename T> void read(T &a)
	{
		a=0;
		int f=1;
		char c=getchar();
		while(!isdigit(c))
		{
			if(c=='-')
			{
				f=-1;
			}
			c=getchar();
		}
		while(isdigit(c))
		{
			a=a*10+c-'0';
			c=getchar();
		}
		a=a*f;
	}
	template <typename T> void write(T a)
	{
		if(a<0)
		{
			a=-a;
			putchar('-');
		}
		if(a>9)
		{
			write(a/10);
		}
		putchar(a%10+'0');
	}
	template <typename T> void writeln(T a)
	{
		write(a);
		puts("");
	}
}
int n,ans;
string a,b,c;
int main()
{
	cin>>n>>a>>b>>c;
	for(int i=0;i<n;i++)
	{
		if(a[i]==b[i]||a[i]==c[i]||b[i]==c[i])
		{
			if(!(a[i]==b[i]&&b[i]==c[i]))
			{
				ans++;
			}
		}
		else
		{
			ans+=2;
		}
	}
	cout<<ans;
}