#include<stdio.h>

long i, j, p, nr;
FILE *fin, *fout;

int main()
{
	fin = fopen("fact.in", "rt");
	fout = fopen("fact.out", "wt");

	fscanf(fin, "%ld", &p);

	i = 0;
	while(nr < p)
	{
		i++;
		nr = 0;

		j = 5;
		while(j <= i)
		{
			nr += i / j;		
	
			j *= 5;
		}
	}

	if(nr > p)
		fprintf(fout, "-1\n");
	else
		fprintf(fout, "%ld\n", i);

	return 0;
}