#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
typedef long long ll;
ll n;
ll check(ll nr){
    ll s = 0;
    for(ll i = 5;i <= nr;i*=5){
        s+=nr/i;
    }
    return s;
}
ll bs(ll l,ll r){
    if(l == r)return l;
    ll mij = (l + r)/2;
    if(check(mij) >= n){
        return bs(l,mij);
    }else return bs(mij + 1,r);
}
int main()
{
    fin>>n;
    //fout<<check(500000000);
    fout<<bs(1,400000015);
    return 0;
}