#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<map>
#include<set>
#include<map>
#include<list>
#include<queue>
#include<stack>
#include<vector>
using namespace std;
long long N;
long long O,I2;
long long n,sum,i; 
long long maxs;
string s,ss;
int main()
{
    cin>>n;
    cin>>s;
    for (i=0;i<n;i++)
    {
        if (s[i]=='I')I2++;
    }
    for (i=0;i<n;i++)
    {
        if (s[i]=='N')N++; 
        if (s[i]=='O')sum+=N*I2;
        if (s[i]=='I')I2--;
        maxs=max(maxs,N*I2);
    }
    //cout<<sum<<endl;
    /*for (i=0;i<n;i++) cout<<N[0][i]<<" "; cout<<endl;
    for (i=0;i<n;i++) cout<<I[0][i]<<" "; cout<<endl;
    for (i=0;i<n;i++) cout<<I[1][i]<<" "; cout<<endl;*/
    long long mmax=sum+maxs;//新增O 
    
    n++;//新增N 
    ss=s;//存原始串。 
    s='N'+ss;
    sum=0;
    N=0;I2=0;
    for (i=0;i<n;i++)
    {
        if (s[i]=='I')I2++;
    }
    for (i=0;i<n;i++)
    {
        if (s[i]=='N')N++; 
        if (s[i]=='O')sum+=N*I2;//求和
        if (s[i]=='I')I2--;
    }
    //cout<<sum<<endl;
    mmax=max(mmax,sum);
    //新增一个N
    
    
    //新增一个I
    s=ss+'I';
    sum=0;
    N=0;I2=0;//记得初始化！
    for (i=0;i<n;i++)
    {
        if (s[i]=='I')I2++;
    }
    for (i=0;i<n;i++)
    {
        if (s[i]=='N')N++; 
        if (s[i]=='O')sum+=N*I2;
        if (s[i]=='I')I2--;
    }
    mmax=max(mmax,sum);
    //cout<<sum<<endl;
    cout<<mmax;
    return 0;
}