#include <fstream>

using namespace std;

int p,i,v[50001],u,s,p2,ap,x,m,sum;

ifstream fin ("fact.in");

ofstream fout("fact.out");

int main (){

    fin>>p2;
    if (p2 == 0){
        fout<<1;
        return 0;
    }
    sum = 0;
    for (i=1;i<=5*p2;i++){
        x = i;
        ap = 0;
        while (x % 5 == 0){
            ap++;
            x/=5;
        }
        v[i] = sum + ap;
        sum = v[i];
    }

    p = 1;
    u = 5*p2;
    while (p <= u){
        m = (p+u)/2;
        if (v[m] < p2)
            p = m+1;
        else
            u = m-1;
    }
    fout<<p;


    return 0;
}