#include<fstream> 
using namespace std;  
long long putere(long long x)
{
	 if(x/5>0) return x/5+putere(x/5);
	 else return 0;
}

int caut(long long i, long long j, long long x)
{
	 if(i<j)
	 {if(x==putere(5*((i+j)/2))) return 5*((i+j)/2);
	    else if(x<putere(5*((i+j)/2))) return caut(i,(i+j)/2,x);
	       else return caut((i+j)/2+1,j,x);
	 }
      else return -1;	 
}
int main() 
{ 
     long long p,n=0,; 
     ifstream f("fact.in");      
     ofstream g("fact.out"); 
     f>>p;    
	 if(p==0) n=1; 
        else n=caut(1,500000000,p);
	 g<<n;     
     return 0; 
}