#include<fstream.h>
int main()
{
unsigned long long int n=0,p,i=1;
ifstream f("fact.in");
ofstream g("fact.out");
f>>p;n++;
while(p!=0)
	{
	n++;
	i=i*n;
	if(i%10==0)
		{
		i=i/10;
		p--;
		}
	}
g<<n;
return 0;
}