#include <fstream>

using namespace std;

ifstream cin("fact.in");
ofstream cout("fact.out");

int nz (int n)
{
    int r=0, f=5;
    while (f<=n)
    {
        r+=n/f;
        f*=5;
    }
    return r;
}

int cautbin(int left, int right, int p)
{
    int mid,temp,k=-1;

    while( left <= right )
    {
        mid=(left+right)/2;
        temp=nz(mid);
        if(temp==p)
        {
            k=mid;
            right=mid-1;
        }
        else
            if(temp>p)
            right=mid-1;
        else
            left=mid+1;
    }
    return k;
}
long long n,p;
int main()
{
    cin>>p;
    cout<<cautbin(1, 2100000000 , p);
    return 0;
}