#include<fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p,mid,st,dr;

int zero(int i){
    int z=0;
    int p=5;
    while(p<=i){
        z+=i/p;
        p*=5;
    }
    return z;
}

int main(){
    fin>>p;
    st=1;
    dr=p*5;
    while(st<=dr){
        mid=(st+dr)/2;
        if(zero(mid)>=p){
            dr=mid-1;
        }
        else
            st=mid+1;
    }
    if(zero(st)==p)
        fout<<st;
    else
        fout<<-1;
    return 0;
}