#include<iostream>   
#include<fstream>   
    using namespace std;   
                 ifstream f("fact.in");   
                 ofstream g("fact.out");   
unsigned long long func(unsigned long long c)   
{   
unsigned long long nrz=0,i=1,aux;   
while(aux!=0)   
{aux=c;   
for(int l=1;l<=i;l++)   
aux/=5;   
nrz+=aux;i++;}   
return nrz;   
             }   
unsigned long long a=0,b=100000000,p,j,c,k,sol;   
  
int main()   
{   
    f>>p;   
    f.close();   
    do  
    {   
         c=(a+b)/2,k=func(c);   
         if (k==p) {sol=c;break;}   
         if (k>p) b=c-1;   
              else a=c+1;}   
              while(a<b);   
for(j=a;j<c;j++)   
if (func(j)==p) {sol=j;break;}   
	g<<sol;   
   g.close();    
    return 0;   
    }