#include<bits/stdc++.h>
    #define intw long long
    #define re register
    #define il inline
    #define inf 1e18
    #define eps 1e-15
    #define ll long long
    #define mod 998244353
    #define bianli for(int i=head[x];i;i=a[i].next)
    #define QWQ cout<<"qwq";
    #define me(qw) memset(qw,0,sizeof(qw));
    #define meinf(qw) memset(qw,0x3f,sizeof(qw));
    using namespace std;
	const int maxn=5e3+5;
	int f[maxn][maxn],ans;
    char a[maxn],b[maxn],p;
	signed main(){
	freopen("palin.in", "r", stdin);
	freopen("palin.out", "w", stdout);
	int n;
	cin>>n;
	for(int i=1;i<=n;i++)cin>>p,a[i]=p;
	for(int i=1;i<=n;i++)b[i]=a[n+1-i];
	for(int i=1;i<=n;i++)
	for(int j=1;j<=n;j++){
	if(a[i]==b[j])
	f[i][j]=f[i-1][j-1]+1;
	else f[i][j]=max(f[i-1][j],f[i][j-1]);
	ans=max(ans,f[i][j]);
	}
	cout<<n-ans;
	return 0;
}