include <stdio.h>

int main() {

int a, c;
scanf("%d", &a);
c = a / 7;

if (a % 3 == 0) {

	if (a % 7 == 0) {
		printf("%d", c);
	} else {
		printf("-1" );
	}

} else {
	printf("-1");
}

return 0;

}