#include<bits/stdc++.h>
using namespace std;
int n;
int tong[105],sum;
string s;
int main(){
	cin>>n;
	cin>>s;
	int len=s.size();
	if(len%n!=0){
		cout<<-1;
		return 0;
	}
	int zifu=len/n;
	for(int i=1;i<=zifu;i++){
		memset(tong,0,sizeof(tong));
		for(int j=i;j<=len;j+=zifu){
			tong[s[j-1]-'a']++;
		}
		int maxn=-1e5;
		for(int j=0;j<=50;j++){
			maxn=max(maxn,tong[i]);
		}
		sum+=n-maxn;
	}
	cout<<sum;
	return 0;
}

AND

#include<bits/stdc++.h>
using namespace std;
int n;
int tong[105],sum;
string s;
int main(){
	cin>>n;
	cin>>s;
	int len=s.size();
	if(len%n!=0){
		cout<<-1;
		return 0;
	}
	int zifu=len/n;
	for(int i=1;i<=zifu;i++){
		memset(tong,0,sizeof(tong));
		for(int j=i;j<=len;j+=zifu){
			tong[s[j-1]-'a']++;
		}
		int maxn=-1e5;
		for(int i=0;i<=50;i++){
			maxn=max(maxn,tong[i]);
		}
		sum+=n-maxn;
	}
	cout<<sum;
	return 0;
}