#include <fstream>

int minim(int a, int b)
{
	return a<b?a:b;
}
int nrDoi(int n)
{
	int counter = 0;

	while(n % 2 == 0 && n > 0)
	{
		counter++;
		n /= 2;
	}
	return counter;
}

int nrCinci(int n)
{
	int counter = 0;

	while(n % 5 == 0 && n > 0)
	{
		counter++;
		n /= 5;
	}
	return counter;
}

int nrZero(int p)
{
	int nrC = 0, nrD = 0;
	int i = 0;
	while(minim(nrC, nrD) != p)
	{
		i++;
		nrC += nrCinci(i);
		nrD += nrDoi(i);
	}
	return i;
}

int main()
{
	int P;
	FILE* fin = fopen("factorial.in","r");
	FILE* fout = fopen("factorial.out","w");
	fscanf(fin,"%d", &P);
	fprintf(fout,"%d",nrZero(P));
	return 0;
}