#include <fstream>

using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");

int main()
{
long long int p,z=1,k=0,x,i;
 in>>p;
 for(i=1;i<=999999;i++){
					z=z*i;
					x=z;
					while(x)
						{
					    if(x%10!=0) break;
						       else k++;
						x=x/10;
					    }
					if(k==p) { out<<i;
					           break;}
					
					     else k=0;       
                      }
}