#include<bits/stdc++.h>
using namespace std;
#define int long long
int n;
string inps;
int ar[510];
int dp[410][410][410][3];
vector<int>e[3];
int difc[510][3];
void upd(int A,int B,int C,int tl,int a,int b,int c,int tll){
if(A>e[0].size()){return;}
if(B>e[1].size()){return;}
if(C>e[2].size()){return;}
int cal=dp[a][b][c][tll];
int i=A+B+C;
cal-=i;
int pl;
int us=0;
if(tl==0){pl=e[0][A-1];us=max(B-difc[pl][1],0ll)+max(C-difc[pl][2],0ll); }
if(tl==1){pl=e[1][B-1];us=max(A-difc[pl][0],0ll)+max(C-difc[pl][2],0ll); }
if(tl==2){pl=e[2][C-1];us=max(B-difc[pl][1],0ll)+max(A-difc[pl][0],0ll); }
cal+=pl;
cal+=us;
dp[A][B][C][tl]=min(dp[A][B][C][tl],cal);
}
signed main(){
cin>>n>>inps;
for(int i=0;i<n;i++){
if(inps[i]=='R'){
ar[i+1]=0;
}
if(inps[i]=='G'){
ar[i+1]=1;
}
if(inps[i]=='Y'){
ar[i+1]=2;
}
}
for(int i=1;i<=n;i++){
e[ar[i]].push_back(i);
}
for(int i=1;i<=n;i++){
for(int j=1;j<=i;j++){
if(ar[j]!=ar[i]){
difc[i][ar[j]]++;
}
}
}
for(int a=0;a<=e[0].size();a++){
for(int b=0;b<=e[1].size();b++){
for(int c=0;c<=e[2].size();c++){
dp[a][b][c][0]=1e9;
dp[a][b][c][1]=1e9;
dp[a][b][c][2]=1e9;
}
}
}
if(e[0].size()){
dp[1][0][0][0]=e[0][0]-1;
}
if(e[1].size()){
dp[0][1][0][1]=e[1][0]-1;
}
if(e[2].size()){
dp[0][0][1][2]=e[2][0]-1;
}
for(int a=0;a<=e[0].size();a++){
for(int b=0;b<=e[1].size();b++){
for(int c=0;c<=e[2].size();c++){
upd(a,b,c+1,2,a,b,c,0);
upd(a,b+1,c,1,a,b,c,0);
upd(a+1,b,c,0,a,b,c,1);
upd(a,b,c+1,2,a,b,c,1);
upd(a+1,b,c,0,a,b,c,2);
upd(a,b+1,c,1,a,b,c,2);
}
}
}
int ans=min({dp[e[0].size()][e[1].size()][e[2].size()][0],dp[e[0].size()][e[1].size()][e[2].size()][1],dp[e[0].size()][e[1].size()][e[2].size()][2]});
if(ans==1e9){ans=-1;}
cout<<ans<<endl;
int a;int b;int c;
return 0;
while(cin>>a>>b>>c){
cout<<dp[a][b][c][0]<<" "<<dp[a][b][c][1]<<" "<<dp[a][b][c][2]<<endl;
}
}
