#include<bits/stdc++.h>
#include<algorithm>
#include<random>
#include<chrono>
#include<cstdlib>
#include<ctime>
#include<numeric>
#include<vector>
#include<stack>
#include<map>
#include<set>
#include<queue>
#include<iomanip>
#define int long long
#define ll long long
#define L LLONG_MAX
#define fi first
#define se second
#define pii pair<int,int>
#define pll pair<long long,long long>
#define sz(a) ((int)a.size())
#define FOR(i,j,k) for(int i=j;i<=k;i++)
#define REP(i,k,j) for(int i=k;i>=j;i--)
#define FORD(i,a) for(auto i:a)
#define MASK(i) ((1)<<(i))
#define rngdcl mt19937_64 rng(chrono::steady_clock::now().time_asince_epoch().count())
#define random(l,r) ((l)+(rng()%(r-l+1)))
using namespace std;
const int nmax=2e5+1;
int n;
string s;
int J[nmax],O[nmax],I[nmax];
map<pair<pair<int,int>,int>,int> m;
void input()
{
cin >> n >> s;
}
void sub1()
{
s='0'+s;
int ans=0;
FOR(i,1,n-1) FOR(j,i+1,n)
{
int a=0,b=0,c=0;
FOR(k,i,j)
{
if(s[k]=='J') a++;
if(s[k]=='O') b++;
if(s[k]=='I') c++;
}
if(a==b && b==c) ans=max(ans,(j-i+1));
}
cout << ans;
}
void sub2()
{
int ans=0;
FOR(i,0,sz(s)-1)
{
if(i!=0)
{
J[i]+=J[i-1];
O[i]+=O[i-1];
I[i]+=I[i-1];
}
if(s[i]=='J') J[i]++;
if(s[i]=='O') O[i]++;
if(s[i]=='I') I[i]++;
int mn=min({J[i],O[i],I[i]});
if(m.count({{J[i]-mn,O[i]-mn},I[i]-mn})) ans=max(ans,mn-m[{{J[i]-mn,O[i]-mn},I[i]-mn}]);
else m[{{J[i]-mn,O[i]-mn},I[i]-mn}]=mn;
}
if(m.count({{0,0},0})) ans=max(ans,m[{{0,0},0}]);
cout << ans*3;
}
signed main()
{
//freopen(".inp", "r", stdin);
//freopen(".out", "w", stdout);
ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
input();
if(n<=200) sub1();
else sub2();
}
