#include<cstdio>
#include<cmath>

int isprim(int x)
{
    if((x & 1) == 0)
    {
        return 0;
    }

    int xx = (int)sqrt(x);
    for(int i = 3; i<= xx; i+=2)
    {
        if(x%i == 0)
        {
            return 0;
        }
    }

    return 1;
}

int main()
{
    //freopen("A.in","r",stdin);
    //freopen("A.out","w",stdout);

    int n = 0;
    scanf("%d",&n);

    if(n == 2)
    {
        printf("1\n");
    }
    else if(n== 3)
    {
        printf("2\n");
    }
    else if(n == 4)
    {
        printf("2\n");
    }
    else
    {
        if(isprim(n))
        {
            printf("%d\n",n-1);
        }
        else
        {
            printf("0\n");
        }
    }

    return 0;
}