#include<cstdio>
#include<fstream>
using namespace std;

int p;

int bun(int x)
{
	int cont=0;
	int putere=5;
	while(x>=putere)
	{
		cont+=(x/putere);
		putere*=5;
	}
	if (cont>=p) return 1;
	return 0;
}


int main()
{
	ifstream fin("fact.in");
	freopen("fact.out","w",stdout);
	fin>>p;
	
	int s=0,d=1000000,m;
	int rez=-1;
	while(s<=d)
	{
		m=(s+d)>>1;
		if(bun(m)) 
			{
				rez=m;
				d=m-1;
			}
		else s=m+1;
	}
	
	printf("%d\n",rez);
	return 0;
}