#include<cstdio>
using namespace std;
int zero(int n)
{
	int r=0;
	while(n>=5)
	{
		r+=n/5;
		n/=5;
	}
	return r;
}
int cout(int p)
{
	int i=0;
	int pas=1<<29;
	while(pas)
	{
		if(zero(i+pas)<p)
			i+=pas;
		pas/=2;
	}
	return 1+i;
}
int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);\
	int n;
	scanf("%d",&n);
	printf("%d",cout(n));
	return 0;
}