#include<fstream>
using namespace std;
int mij,li=1,lf,p;
unsigned int ok=0;
ifstream f("fact.in");
ofstream g("fact.out");
 int nz(int n){
	unsigned int y=0,c=5;
	while(n>=c){
		y+=n/c;
		c*=5;
	}
	return y;
}
int main(){
	f>>p;
	lf=5*p;
	while(li<=lf){
		mij=(li+lf)/2;
		if(nz(mij)<p)
			li=mij+1;
		else
			lf=mij-1;
	}
	if(nz(li)!=p)
		g<<-1;
	else
		g<<li;
	
	return 0;
}