#include <stdio.h>
#define INFILE "fact.in"
#define OUTFILE "fact.out"

int P;

int digits(int N)
{
	int dig = 0;
	do {
		dig++;
		N /= 10;
	} while (N);
	return dig;
}

int factorial(int N)
{
	int i, j;
	int count = 0;
	for (i=5; i<=N; i+=5) {	
			j = i;
			while (!(j%5)) {
				j /= 5;
				count++;
			}
		}
	return count;
}

int cauta(int target, int low, int high)
{
	while (low < high) {
		int mid = (low + high)/2;
		int f = factorial(mid);
		if (target == f)
			return mid;		
		if (target < f) 
			high = mid-1;
		else
			low = mid+1;
	}
}
	

int main()
{
	freopen(INFILE, "r", stdin);
	freopen(OUTFILE, "w", stdout);
	scanf("%d", &P);
	if (P == 0) {
		printf("1");
		return 0;
	}
	int low = 0;
	int high = 40000006; 
	int result = cauta(P, low, high);
	if (result == -1) {
		printf("-1");
		return 0;
	}
	while (result % 5)
		result--;
	printf("%d\n", result);
	return 0;
}