#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");

    long p,l=0,r=1000000000,i,m,aux=-1,s=0;
    f>>p;
    if(p==0)
        aux=1;
    else
    while(l<=r)
    {
        m=(l+r)/2; s=0; i=5;
        while(m/i>=1)
        {
            s+=m/i;
            i*=5;
        }
        if(s==p)
        {
            aux=m;
            r=m-1;
        }
        else
            if(s>p)
               r=m-1;
            else
                l=m+1;
    }
    g<<aux;
    return 0;
}