#include <fstream>

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long p,l,x,nr,y,i,u,z,m;
int zero(int x)
{
    int nr=0,l=5;
    while(l<=x)
    {
        nr=nr+x/l;
        l=l*5;
    }
    return nr;
}
int main()
{
    f>>z;
    p=1;
    u=z*5;
    while(p<=u)
    {
        m=(p+u)/2;
        if(zero(m)>=z) u=m-1;
        else p=m+1;
    }
    g<<u+1;
    return 0;
}