#include<stdio.h>
#define NMax 100000000

long i, j, n;

long f(int x)
{
	long a = 5, rez = 0;
	while(x / a) {
		rez += x / a;
		a *= 5;	
	}

	return rez;
}

int main()
{	
	freopen("fact.in", "rt", stdin);
	freopen("fact.out", "wt", stdout);
	
	scanf("%ld", &n);
	
	if(n == 0) printf("0\n");
	else
	{
		int inc = 0, sf = NMax, mid, val;
		bool ok = false;
		while (inc <= sf && !ok) {
			mid = (inc + sf) / 2;
			val = f(mid);
			
			if(val < n) inc = mid + 1;
			else if(val > n) sf = mid - 1;
			else ok = true;
		}
		
		if(ok)			
		{
			while (mid % 5) mid--;
			printf("%d", mid);
		}
		else printf("-1\n");
	}
	
	return 0;
}