#include <fstream>

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int n,i,j,p;
int cautbin(long long a,long long b)
{
    if(a>b)
        return -1;
    int m=(a/5+b/5)/2;
    m*=5;
    int pa,pb,pm;
    pa=a/5+(a/5)/5;
    pb=b/5+(b/5)/5;
    pm=m/5+(m/5)/5;
    if(pm>n)
        return cautbin(a,m-5);
    else
        if(pm<n)
            return cautbin(m+5,b);
        else
            return m;
}
int main()
{
    f>>n;
    if(n==0)
        g<<"1"<<'\n';
    else
    {
        g<<cautbin(0,n*5)<<'\n';
    }
    return 0;
}