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

ifstream in("fact.in");
ofstream out("fact.out");

const int val=500000000;

long long fact(long long n)
{
    long long s=0,p=1;
    while(n>=p)
    {
        p*=5;
        s+=n/p;
    }
    return s;
}
int main()
{
    int p;
    in>>p;
    long long st=0,dr=val,mij;
    long long gasit=-1;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(fact(mij)<p)
            st=mij+1;
        else if(fact(mij)>=p)
            dr=mij-1,gasit=mij;
    }
    if(p>0)
        out<<gasit;
    else
        out<<1;
    return 0;
}