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

long long mij,nr,p,k;
long zerouri(long long x)
{
    p=5;
    nr=0;
    while(p<=x)
    {
        nr=nr+x/p;
        p=p*5;
    }
    return nr;
}
long long cautarez (long long l, long long r)
{
    while(l<=r)
    {
        mij=l+(r-l)/2;
        if(zerouri(mij)>=k){
            if(zerouri(mij-1)<k || mij==l) return mij;
            else r=mij-1;
        }
        else
        l=mij+1;
    }
    return -1;
}
int main()
{   ifstream cin("fact.in");
    ofstream cout("fact.out");
    cin>>k;
    cout<<cautarez(1,1000000000);
    return 0;
}