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

int n;
unsigned long long p = 1;
int isPrime = 1;

int main() {
    scanf("%d", &n);

    switch(n) {
        case 2: {
            printf("%1");
        break; }
        case 3: case 4: {
            printf("2");
        break;}
    default:
        int sqrtt = sqrt(n);
        for(int d = 2; d <= sqrtt; ++d) {
            if(!(n % d)) {
                isPrime = 0;
                break;
            }
        }
        if(isPrime) printf("%d", n - 1);
        else printf("0");
        break;
    }

    return 0;
}