#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int main()
{
    int p,n,x,nr,d;
    fin>>p;
    if(p==0){cout<<1;return 0;}
    nr=0;
    for(n=p*4;nr!=p;++n)
    {
        nr=0;x=n;d=5;
        while(d<=n)
        {
            nr+=n/d;
            d*=5;
        }
    }
    fout<<n-1;
}