#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

int n,i,j,p,k,smax,med,st,dr;
int nr(int r)
{
    int nr=0,t=5;
    while(r/t)
    {
        nr+=r/t;
        t*=5;
    }
    return nr;
}

int main()
{
    fin>>n;
    st=1;
    dr=10000000;
    while(st<=dr)
    {
        med=(st+dr)/2;
        smax=nr(med);

        if(smax>n)
            dr=med-1;
        else
            st=med+1;
    }

    fout<<dr-dr%5;

    return 0;
}