#include <fstream>
#include <cmath>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int p,x,st=1,dr=100000000,fact,mij;
int main()
{
    in>>p;
    while (st<dr)
    {
        fact=0;
        mij=(st+dr)/2;
        fact+=mij/5;
        x=log2(mij)/log2(5);
        fact-=(x-1);
        fact+=(x*(x+1))/2-1;
        if (fact<p)
            st=mij+1;
        else
            dr=mij;
    }
    out<<st;
}