#include<fstream.h>
 int desc(long n){
     long p=0,r;
     while(n>0) {r=n%5;n=n/5;p+=(r==0);}
     return p;
 }    
 int main(){
     long p;
     long long n=5;
     ifstream f("fact.in");
     ofstream g("fact.out");
     f>>p;
     while(p>0){
         p-=desc(n);
         n+=5;
     }
     if(p<0) g<<-1;
     else
     g<<n-5;
     g<<"\n";
     g.close();
     return 0;
 }