#include <bits/stdc++.h>

using namespace std;

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

unsigned long long n,nr,nrk,vad,i;
/*
int cbin(int x)
{
    long long msk,pos=0,c=0;
    for(msk=1<<20;msk>0;msk/=2)
    {
        if(pos+msk<=2*n && sume[pos+msk]-sume[indice-1]<=x)
        pos+=msk;
    }
    while(sume[pos]-sume[indice-1]<=x)
    pos++;
    return pos;
}*/

int main()
{
    in>>n;
    nr=0;
    nrk=25;
    vad=1;
    for(i=1; i<=n; i++)
    {
        nr+=5;
        if(nr==nrk)
        {
            i+=vad;
            vad++;
            nrk*=5;
        }
    }
    if(nr==0)
        nr=1;
    out<<nr;
    return 0;
}