#include<bits/stdc++.h>
using namespace std;
 
using ll=long long;
using pp=pair<int,int>;
#define sr string 
#define vc vector
#define db double
#define fi first
#define se second
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define pb push_back
#define all(v) v.begin(),v.end()
#define pque priority_queue
#define bpc(a) __builtin_popcount(a)
int main(){
	int n; sr s;cin>>n>>s;
	n*=3;
	vc v(3,vc<int>(3,0));
	sr con="con";
	rep(i,n)rep(j,3)if(s[i]==con[j])v[i%3][j]++;
	int ans=0;
	rep(i,3){
		int mn=n;
		rep(j,3)mn=min(mn,v[i][j]);
		ans+=mn;
	}
	cout<<ans;
}