include <stdio.h>

int main() {

int a, b, c;
scanf("%d", &a);
if (a % 21 == 0) {
	b = a / 7;
	printf("%d", b);
} else  {
	(a % 21 != 0);
	printf("-1");
}
return 0;

}#include <stdio.h>

int main() {

int a, b, c;
scanf("%d", &a);
if (a % 21 == 0) {
	b = a / 7;
	printf("%d", b);
} else  {
	(a % 21 != 0);
	printf("-1");
}
return 0;

}

include <stdio.h>

int main() {

int a, b, c;
scanf("%d", &a);
if (a % 21 == 0) {
	b = a / 7;
	printf("%d", b);
} else  {
	(a % 21 != 0);
	printf("-1");
}
return 0;

}#include <stdio.h>

int main() {

int a, b, c;
scanf("%d", &a);
if (a % 21 == 0) {
	b = a / 7;
	printf("%d", b);
} else  {
	(a % 21 != 0);
	printf("-1");
}
return 0;

}

include <stdio.h>

int main() {

int a, b, c;
scanf("%d", &a);
if (a % 21 == 0) {
	b = a / 7;
	printf("%d", b);
} else  {
	(a % 21 != 0);
	printf("-1");
}
return 0;

}