#include<fstream>
#define LL long long
using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
LL A=0,B=2000000000,C,P,R;
LL f(LL n) {
   	LL S=0;
	   while(n>0) {
	   		S+=n/5;
			n=n/5;
			}
	return S;
}
int main() {
	cin>>P;
	  while(B-A>1) {
	           C=(A+B)/2;
	           if(f(C)<P)
	                 A=C+1;
	           if(f(C)>P)
			         B=C-1;  
			if(f(C)==P) { if(f(C-1)==P) {
						        while(f(C)==P) C--;
			                    C++;
								}	   
						  cout<<C;
				             return 0; }
  }						  	  
 cout<<"-1";  
 return 0;
}