#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <math.h>

unsigned int save_tens(unsigned long *p)
{
	unsigned int nr = 0;

	while (*p % 10 == 0)
	{
		*p = *p / 10;
		nr++;
	}
	return nr;
}

unsigned long ipow(unsigned long base, unsigned long exp)
{
	int result = 1;
	while (1)
	{
		if (exp & 1)
			result *= base;
		exp >>= 1;
		if (!exp)
			break;
		base *= base;
	}

	return result;
}

unsigned int len(unsigned int n)
{
	unsigned int count = 0;
	while (n)
	{
		n = n / 10;
		count++;
	}
	return count;
}

int main()
{
	FILE* f = fopen("fact.in", "rt");
	unsigned long n, p=1, i=2, count=0;
	
	fscanf(f, "%lu", &n);

	while (count != n)
	{
		p = (p * i) % 1000;
		count = count + save_tens(&p);
		i++;
	}

	f = fopen("fact.out", "wt");

	fprintf(f, "%lu \n", i-1);
	fflush(stdout);

	fclose(f);
	return 0;
}