#include <fstream>
using namespace std;
int legendre(long long n) {
    long long p=5;
    int cnt=0;
    while (p<=n) {
        cnt=cnt+n/p;
        p=p*5;
    }
    return cnt;
}
ifstream cin("fact.in");
ofstream cout("fact.out");
int main() {
    long long P;
    cin>>P;
    if(P==0) {
        cout<<1;
    }
    else{
        long long st=1, dr=5*P;
        long long r=-1;
        while (st<=dr) {
            long long mid=(st+dr)/2;
            long long val=legendre(mid);
            if (val==P) {
                r=mid;
                dr=mid-1;
            }
            else if(val<P) {
                st=mid+1;
            }
            else {
                dr=mid-1;
            }
        }
        cout<<r;
    }
}