#include <iostream>
#include <algorithm>
using namespace std;

int verif(int x)
{
    int i;
    if(x==2 || x==3 || x==5 || x==7)
        return 1;
    if(x%2==0)
        return 0;
    for(i=3;i*i<=x;i+=2)
        if(x%i==0)
            return 0;
    return 1;
}

int main()
{
    int n;
    cin>>n;
    if(n==4)
        cout<<2;
    else
        if(verif(n))
            cout<<n-1;
        else
            cout<<0;
    return 0;
}