#include<bits/stdc++.h>
using namespace std;


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


std::pair<int,int> get_div(int a)
{
    int f=0,t=0;

    while(a%2==0)
    {
        a/=2;
        t++;
    }
    while(a%5==0)
    {
        f++;
        a/=5;
    }
    return {f,t};

}

int solve()
{
    int div5,div2;
    int iter=1;
    while(min(div5,div2)<n)
    {
        iter++;

        std::pair<int,int>divv=get_div(iter);

        div5+=divv.first;
        div2+=divv.second;
    }

    return iter;
}

int main()
{
    in>>n;
    out<<solve();
}