#include <fstream>

using namespace std;
    ifstream cin("fact.in");
    ofstream cout("fact.out");

int cz(int n)
{
      int put=5;
      int sum=0;
      while(put<=n)
      {
            sum+=n/put;
            put*=5;
      }
      return sum;
}
int main()
{
    int l=0,r=500000000,sol=-1,n;
    cin>>n;
    while(l<=r)
    {
          int m=(l+r)/2;
          if(cz(m)<n)
          {
                l=m+1;
          }
          else if(cz(m)==n)
          {
                sol=m;
                r=m-1;
          }
          else
          {
                r=m-1;
          }
    }
    cout<<sol;
    return 0;
}