#include<fstream.h>
 ifstream f("fact.in");
  ofstream g("fact.out");
    long n,nr;
	int corect(int nr){
		int put=0;
		while(nr){
			nr=nr/5;
			put+=nr;
		}
		return put;
	}
	int cb(int in,int sf){
		while(in<sf){
			int mij=(in+sf)/2,put;
			put=corect(mij);
			if(put==n) return mij;
			else 
			if(put>n) sf=mij-1;
			else in=mij+1;
		}
		return -1;
	}
	int main(){
		f>>n;
		if(n==0) g<<"1\n";
		else{
		    nr=cb(1,100000000);
			if(nr<0) g<<nr;
			else
			    g<<nr-nr%5<<'\n';
		}
		g.close();
		return 0;
	}