#include <iostream>
#include <fstream>
using namespace std;
int j, p,i,s,d,m,k;
int main()
{
    int sol=-1;
    ifstream f("fact.in");
    f>>p;
    ofstream g("fact.out");
    s=1;d=20000000;
    while(s<d)
    {
        m=(s+d)/2;
        k=0;
        for(j=5;j<=m;j=j*5)
            k=k+m/j;
        if(k==p)
        {
            sol=m;
            sol--;
            d=m-1;
        }
        else if(k>p)
            d=m-1;
        else s=m+1;
    }
    g<<sol;
  return 0;
}