#include <iostream>
#include <fstream>

using namespace std;
const int L=31;
ifstream in("fact.in");
ofstream out("fact.out");
int v[2000000001];
int p18(int r){
int cif=0,c;

    for(c=5;c<r;c+=5)
    while(c%5==0&&c>0){
    cif=cif/5;
    c++;
    }
    return c;
}
int main(){
    int p,i,r=0,pas;

    in>>p;
    pas=1<<L;
    while(pas>0){
    if(p18(r)<p)
    r+=pas;
    pas/=2;
    }
    out<<r;

    return 0;
}