#include <bits/stdc++.h>
using namespace std;
ifstream fin("gard.in");
ofstream fout("gard.out");
int n,i,j,lg,sc,fra,frr,frv,altsc,ci,lgmax=999999;
char sir[100002];
int fr[100002][4];
int main()
{
    fin>>n;
    sc=n/3;
    fin>>sir[0];
    if(sir[0]=='R')
        fr[0][1]=1;
    else if(sir[0]=='V')
        fr[0][2]=1;
    else fr[0][0]=1;
    for(i=1; i<n; ++i)
    {
        fr[i][1]=fr[i-1][1];
        fr[i][0]=fr[i-1][0];
        fr[i][2]=fr[i-1][2];
        fin>>sir[i];
        if(sir[i]=='R')
            fr[i][1]++;
        else if(sir[i]=='V')
            fr[i][2]++;
        else fr[i][0]++;
    }
    //fout<<fr[n-1][0]<<" "<<fr[n-1][1]<<" "<<fr[n-1][2]<<'\n';
    if(fr[n-1][0]==sc && fr[n-1][1]==sc && fr[n-1][2]==sc)
    {
        fout<<0;
        return 0;
    }
    altsc=max(max(fr[n-1][0],sc)-min(fr[n-1][0],sc),max(max(fr[n-1][1],sc)-min(fr[n-1][1],sc),max(fr[n-1][2],sc)-min(fr[n-1][2],sc)));
    //fout<<altsc;
    for(i=0;i<n;++i)
    {
        if(j==0)
            j=i;
        ci=i;
        while((fr[n-1][0]-(fr[j][0]-fr[i-1][0])>sc || fr[n-1][1] - (fr[j][1]-fr[i-1][1])>sc || fr[n-1][2] - (fr[j][2]-fr[i-1][2])>sc) && j<n)
            j++;
        if(j==n)
            continue;
        while((fr[n-1][0]-(fr[j][0]-fr[ci-1][0])<=sc && fr[n-1][1] - (fr[j][1]-fr[ci-1][1])<=sc && fr[n-1][2] - (fr[j][2]-fr[ci-1][2])<=sc) && ci<j)
            ci++;
        ci--;
        lgmax=min(lgmax,j-ci+1);
        i=max(i,ci);
    }
    fout<<lgmax;
    return 0;
}