#include <fstream>

#define drMAX 600000005

using namespace std;

int nrZero(int n){
     int s=0;
    while(n>=5){
        n/=5;
        s+=n;
    }
    return s;
}

int binS(int p)
{
    int st=1, dr=drMAX, poz=-1;
    while(st<=dr){

        int mij=st+(dr-st)/2;
        if(p==nrZero(mij)){
            poz=mij;
        }
        if(p<=nrZero(mij)){
            dr=mij-1;
        }
        else{
            st=mij+1;
        }
    }

    return poz;
}

int main()
{
    ifstream cin("fact.in");
    ofstream cout("fact.out");
    int P;
    cin>>P;
    cout<<binS(P);

    return 0;
}