#include <bits/stdc++.h> using namespace std; using ll=long long; #define f first #define s second #define pii pair<int,int> #define all(a) a.begin(),a.end() #define sz(a) (int)a.size() const int N=405; int n; string s; int cntR,cntG,cntY; int pre[3][N]; //số phần tử X từ 1 ->i; int id[3][N]; //vi tri cua phần tử x thứ i int dp[3][N][N][N]; const int INF=INT_MAX-50; void presolve(){ for(int i=1;i<=n;++i){ for(int j=0;j<3;++j) pre[j][i]+=pre[j][i-1]; if(s[i]=='R'){ ++cntR; ++pre[0][i]; id[0][cntR]=i; } if(s[i]=='G'){ ++cntG; ++pre[1][i]; id[1][cntG]=i; } if(s[i]=='Y'){ ++cntY; ++pre[2][i]; id[2][cntY]=i; } } for (int c = 0; c < 3; ++c) for (int r = 0; r <= cntR; ++r) for (int g = 0; g <= cntG; ++g) for (int y = 0; y <= cntY; ++y) dp[c][r][g][y] = INF; for (int c = 0; c < 3; ++c) dp[c][0][0][0] = 0; } void solve(){ cin>>n>>s; s='%'+s; presolve(); for(int i=0;i<=cntR;++i){ for(int j=0;j<=cntG;++j){ for(int k=0;k<=cntY;++k){ for(int cur=0;cur<3;++cur){ if (dp[cur][i][j][k] == INF) continue; for(int nx=0;nx<3;++nx){ if(cur==nx) continue; if(i==cntR && nx==0)continue; if(j==cntG && nx==1)continue; if(k==cntY && nx==2)continue; int nr=i,ng=j,ny=k; int c=0; if(nx==0){ ++nr; c+=max(0,ng-pre[1][id[0][nr]]); c+=max(0,ny-pre[2][id[0][nr]]); } if(nx==1){ ++ng; c+=max(0,nr-pre[0][id[1][ng]]); c+=max(0,ny-pre[2][id[1][ng]]); } if(nx==2){ ++ny; c+=max(0,ng-pre[1][id[2][ny]]); c+=max(0,nr-pre[0][id[2][ny]]); } dp[nx][nr][ng][ny]=min(dp[nx][nr][ng][ny],dp[cur][i][j][k]+c); } } } } } int res = INF; for (int i = 0; i <= 2; ++i) res = min(res, dp[i][cntR][cntG][cntY]); cout << (res == INF ? -1 : res); } signed main(){ ios_base::sync_with_stdio(0);cin.tie(0); solve(); }