#include <iostream>
#include <fstream>
#include <climits>

using namespace std;

int exp(int x){
    int k=0;
    while (x>0){
        x-=x%5;
        k+=x/5;
        x/=5;
    }
    return k;
}

int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");

    int x,hi=INT_MAX,lo=0,mid;

    in >> x;

    while (hi - lo > 1){
        mid = int((hi+lo)/2);

        if (exp(mid)>=x) hi=mid;
        else lo=mid;
    }

    out << hi;

    return 0;
}