#include <fstream>
#define ll long long
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
ll x(int n)
{   ll s=0,p=5;
    while(p<=n) {s+=n/p; p*=5;}
    return s;
}
int cb(int P)
{   ll st=1,dr=(1LL<<62);
    while(st<=dr)
    {   ll mid=(dr+st)/2;
        ll v=x(mid);
        if(P==v) return mid-mid%5;
        if(P<v) dr=mid-1; else st=mid+1;
    }
    return -1;
}
int P;
int main()
{   f>>P;
    if(P) g<<cb(P)<<'\n'; else g<<"1\n";
    g.close(); return 0;
}