#include <iostream>
#include<fstream>

using namespace std;
ifstream fin(" fact.in");
ofstream fout(" fact.out");
int zero(int n)
{
    double i=5,S=0;
    while(i<=n)
    {
        S+=n/i;
        i*=5;
    }
    return S;
}

int cautare(int st,int dr,int p)
{
    int ok=0,m,val_m,i;
    while(st<=dr && !ok)
    {
        m=(st+dr)/2;
        val_m=zero(m);
        if(p<val_m)
            dr=m-1;
        else if(p>val_m)
            st=m+1;
        else ok=1;
    }

    if(ok==1)
    {for(i=m;i%5!=0;)
    i--;
    return i;
    }

    return -1;
}

int main()
{
   int p;
   fin>>p;
   fout<<cautare(1,100000000000000000000,p);
    return 0;
}