#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int st=1,dr=1<<30,mid,sol;


int cifre(int x)
{
    int i=5,y=0;
    while (i<=x) {
        y+=x/i;
        i*=5;
    }
    return y;

}


int main()
{
    int i,j;
    f>>i;
    while (st<=dr) {
        mid=(st+dr)>>1;
        j=cifre(mid);
        if (j>=i) {
            sol=mid;
            dr=mid-1;
        }
        else
            st=mid+1;
    }
    g<<sol<<'\n';

    return 0;
}