#include<stdio.h>
using namespace std;
unsigned int v(int n,int y)
{int f,s,k;
	f=y;s=0;k=5;
while(n/f>0)
	{
		s=s+n/f;
		f=f*k;
	}
return s;
}

int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
unsigned int x,n;
scanf("%d",&n);
x=1;
if(n!=0)
{
	while(v(x,5)!=n)
	x++;
	printf("%d",x);
}
else
	printf("1");
return 0;
}