#include<fstream.h>
#define N 100000000
long p,i,j,t,s,k,l=0;
int main()
{ifstream f("fact.in");
ofstream g("fact.out");
f>>p;
for(s=1;s<=N;s<<=1);
for(i=0;s;s>>=1)
if(s+i<=N)
       {j=5*(i+s),t=0;
       for(k=5;k<=j;k*=5)
             t=t+j/k;
       if(t<=p)
             i+=s,l=t;}
if(p==0)
       g<<"1";
else
       if(l==p)
               g<<(5*i);
       else
               g<<"-1";
f.close();
g.close();
return 0;}