#include <bits/stdc++.h>
using namespace std;
ifstream f("main.in");
ofstream g("main.out");
int prim(int n)
{
    int d;
    for(d=2;d<=n/2;d++)
        if(n%d==0)
            return 0;
    return 1;
}
int main()
{
    int n,p=1;
    cin>>n;
    if(n%10==0)
    {
        cout<<0;
        return 0;
    }
    if(prim(n))
        cout<<n-1;
    else
    {
        if(n==4)
            cout<<2;
        else
            cout<<0;
    }
    return 0;
}