#include<fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
	
int factorial(int x)
{int P=0;
	for(int i=5;i<=x;i+=5)
		{	P++;
			int ii=i;  
			if(i%25==0)
				while(ii%25==0)
				{
					P++;
					ii=ii/5;
				}
		}
	return P;
}
int main()
{	int P;
	in>>P;
	int  a=0;
	int b=5*P;
	int c=(a+b)/2;
	while(factorial(c)!=P)
		{if(factorial(c)>P) b=c-1;
		else a=c+1;
		c=(a+b)/2;
		if(a>b) {c=-1; break;}
		
		}
c=c-c%5;
if(c==0) c=1;

out<<c;
return 0;
}