#include<fstream>
using namespace std;
int main()
{
	ifstream in("fact.in");
	ofstream out("fact.out");
	int P,n,eror=0,i;
	
	in>>P;
	n=5*P;
	
	for(i=25;i<=n;i+=25)
	{
		if(i%25==0) {eror++; n=n-5*eror;if(i==n) n=-1;}		
		if(i%625==0){eror+=2; n=n-5*eror;if(i==n) n=-1;}
		if(i%3125==0){eror+=3; n=n-5*eror;if(i==n) n=-1;}
		if(i%15625==0){eror+=4; n=n-5*eror;if(i==n) n=-1;}
		if(i%78125==0){eror+=5; n=n-5*eror;if(i==n) n=-1;}
		if(i%390625==0){eror+=6; n=n-5*eror;if(i==n) n=-1;}
	}
if(P=0) out<<"1";
else out<<n;	
	return 0;
}