#include <stdio.h>
 
using namespace std;
 
long long p, n, i, x, ap;
 
int main()
{
    freopen("fact.in", "r", stdin);
    freopen("fact.out", "w", stdout);
 
    scanf("%lld", &p);
 
    n = p;

	while(p%5==0)
		p/=10;
	if(p==0)
	{
		printf("-1");
	} else {
 
    while(p%5==0)
    {
        p/=5;
        ap++;
    }
 
    n -= ap;
 
 
    printf("%d", n * 5);

	}
 
 
    return 0;
}