#include <bits/stdc++.h>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int nz(int nr){
    int cinciput=5,nrzero=0;
    while(cinciput<=nr){
        nrzero+=nr/cinciput;
        cinciput*=5;
    }
    return nrzero;
}
int cb(int p){
    int st=1,dr=500000000,mid,nr,rez=-1;
    while(st<=dr){
        mid=(st+dr)/2;
        nr=nz(mid);
        if(nr==p)
            rez=mid;
        if(nr<p)
            st=mid+1;
        else
            dr=mid-1;
    }
    return rez;
}
int p;
int main()
{
    fin>>p;
    fout << cb(p) << endl;
    return 0;
}