#include<cstdio>
using namespace std;
int p,i,nr;
void read()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%d",&p);
}

int p5(int x)
{
	int cont=0;
	while(x%5==0)
	{
		x/=5;
		cont++;
	}
	return cont;
}

void rez()
{
	for(i=1;;++i)
	{
		nr+=p5(i);
		if (nr>=p)
		{
			printf("%d\n",i);
			break;
		}
	}
}

int main()
{
	read();
	rez();
	return 0; 
}