#pragma GCC optimize("Ofast,unroll-loops")
//#pragma GCC optimize("conserve-stack")
#include<bits/stdc++.h>
#define int long long
#define ll long long
#define down cout<<'\n';
#define debug cout<<" cucuucucuuu",down
#define NHP     ios_base::sync_with_stdio(0);cout.tie(0);cin.tie(0);
#define modwwe  int t;cin>>t; while(t--)
#define bit(i,j) (i>>j&1)
#define sobit(a) __builtin_popcountll(a)
#define task "test"
#define fin(x) freopen(x".inp","r",stdin)
#define fou(x) freopen(x".ans","w",stdout)
#define pb push_back
#define mask(k) (1<<k)
#define mp make_pair
#define checktime   cerr << (double)clock() / CLOCKS_PER_SEC * 1000  << " ms";
using namespace std;
void phongbeo();
const int inf = 1e14;
const int mod2 = 1e9 + 7;
const int  mod1 = 998244353;
const ll base=67;
int add(int x,int y)
{
    if(x+y>=mod2) x-=mod2;
    if(x+y<0) x+=mod2;
    return x+y;
}
struct icd
{
    long double a;
    int b;
};
struct ib
{
    int a;
    int b;
};
struct ic
{
    int a, b, c;
};
struct id
{
    int a, b, c, d;
};
struct ie
{
    int a, b, c, d, e;
 
};
ll n, m, s1, s2, s4, s3, sf, k, s5, s6, mx, s7, s8, s9, mx2, res, dem2 = 0, dem = 0, s33, dem3, dem4, mid, l2, r2, center;
int  i, s10, s12,k1,k2,k3,s11,t,lim,w,l,r;
int kk;
int el = 19;
main()
{
    if(fopen(task".inp","r"))
    {
        fin(task);
        //  fou(task);
    }
    NHP
    /// cin>>s1;
   // modwwe
    phongbeo(),down
    // checktime
}
int a[200001];
int c[3];
map<pair<int,int>,int> cnt;
void phongbeo()
{
 cin>>n;
    string s;
 cin>>s;
 s=" "+s;
  for(int i=1;i<=n;i++){
  if(s[i]=='J')a[i]=0;
  else if(s[i]=='O') a[i]=1;
   else a[i]=2;
     }
cnt[mp(0,0)]=0;
 s4=0;
      for(int i=1;i<=n;i++)
      {
        c[a[i]]++;
        s2=c[0]-c[2];
        s3=c[0]-c[1];
        if(cnt.count(mp(s2,s3)))s4=max(s4,i-cnt[mp(s2,s3)]);
       else cnt[mp(s2,s3)]=i;
      }
       cout<<s4;
}