#include <cstdio>
#include <fstream>
using namespace std;
const long long NMAX=1e7;
long long n2,n5;
void nr(long long n)
{
    while(n%2==0)
    {
        n/=2;
        n2++;
    }
    while(n%5==0)
    {
        n/=5;
        n5++;
    }
}
long long n0(long long n)
{
    long long i;n2=n5=0;
    for(i=1;i<=n;++i)
        nr(i);
    return min(n2,n5);
}
int main()
{
    freopen("factorial.in","r",stdin);
    freopen("factorial.out","w",stdout);
    long long n,st,dr,med,ans,a;
    scanf("%lld",&n);
    st=1;dr=NMAX;
    while(st<=dr)
    {
        med=(st+dr)/2;
        a=n0(med);
        if(a<n)
            st=med+1;
        else
            if(a==n)
            {
                ans=med;
                dr=med-1;
            }
            else
                dr=med-1;
    }
    printf("%lld",ans);
    return 0;
}