#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T> bool maximize(T &a, const T &b){ return (a < b ? a = b, 1 : 0); }
template<class T> bool minimize(T &a, const T &b){ return (a > b ? a = b, 1 : 0); }
#define fi first
#define se second
#define pb push_back
#define ii pair<int, int>
#define all(x) x.begin(), x.end()
#define TASK "nonsense"
/// end of template ///
const int N = 2e5 + 10;
int n;
string s;
namespace sub12
{
bool check()
{
return (n<=4000);
}
const int N = 4000 + 10;
int p[N][3];
void solve()
{
int ans=0;
s=" "+s;
for(int i=1;i<=n;++i)
{
for(int j=0;j<3;++j) p[i][j]=p[i-1][j];
if(s[i]=='J') ++p[i][0];
if(s[i]=='O') ++p[i][1];
if(s[i]=='I') ++p[i][2];
}
for(int l=1;l<=n;++l) for(int r=l;r<=n;++r)
{
if(p[r][0]-p[l-1][0]==p[r][1]-p[l-1][1] && p[r][1]-p[l-1][1]==p[r][2]-p[l-1][2])
maximize(ans,r-l+1);
}
cout<<ans;
}
}
namespace subfull
{
int p[N][3];
string work(int id)
{
string ans;
int a=p[id][0];
int b=p[id][1];
int c=p[id][2];
int diff=-a;
a+=diff;
b+=diff;
c+=diff;
ans+=to_string(a);
ans+='#';
ans+=to_string(b);
ans+='#';
ans+=to_string(c);
return ans;
}
map<string,int> mp;
void solve()
{
mp[work(0)]=0;
int ans=0;
for(int i=1;i<=n;++i)
{
for(int j=0;j<3;++j) p[i][j]=p[i-1][j];
if(s[i]=='J') ++p[i][0];
if(s[i]=='O') ++p[i][1];
if(s[i]=='I') ++p[i][2];
string cur=work(i);
if(mp.count(cur)) maximize(ans,i-mp[cur]);
else mp[cur]=i;
}
cout<<ans;
}
}
void solve()
{
cin>>n>>s;
if(sub12::check()) return void(sub12::solve());
return void(subfull::solve());
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
// freopen(TASK".inp","r",stdin);
// freopen(TASK".out","w",stdout);
int testcase=1;
// cin>>testcase;
while (testcase--)
solve();
return 0;
}
