#include<stdio.h>
#include<math.h>

int n,i,rad;

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

    scanf("%d",&n);
    if(n == 4)
    {
        printf("2\n");
        return 0;
    }
    rad = sqrt(n);
    for(i = 2; i <= rad; i++)
        if(n % i == 0)
        {
            printf("0\n");
            return 0;
        }
    printf("%d\n",n - 1);

    return 0;
}