#include <iostream>

using namespace std;

int solve()
{
    int n;
    cin>>n;
    if(n == 4)
        return 2;
    for(int d = 2; d*d <= n; d++)
        if(n%d == 0)
            return 0;
    return n-1;
}

int main()
{
    cout<<solve()<<'\n';
    return 0;
}