#include <fstream>

using namespace std;

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

int main()
{
	unsigned long int p,n,nr0;
	unsigned int nr2,nr5;
	in>>p;
	n=1;
	nr0=0;
	while(nr0<=p){nr2=0;
	              nr5=0;
                  nr0=0;	
		          for(unsigned int i=1;i<=n;i++){if(i%10==2)nr2++;
	                                             if(i%10==5)nr5++;
				                                 if(i%10==0)nr0++;
				                                 if(nr2==nr5){nr0++;
												              nr2--;
												              nr5--;}
				  }
				  n++;
				  }
	out<<nr0;
}