#include <fstream>
#include <cmath>
#include <algorithm>
using namespace std;
ifstream fin("factorial.in");
ofstream fout("factorial.out");
int n,z,i,a,j,c,dr,st,p,mid;


int main(){
    fin>>p;
    st=1;
    dr=500000000;
    while(st<=dr){
        mid=(st+dr)/2;
        z=0;
        c=5;
        a=1;
        while(a!=0){
            a=mid/c;
            c=c*5;
            z=z+a;
        }


        if(z>=p){
            dr=mid-1;
        }
        else{
            st=mid+1;

        }

    }
    if(p==0){
        fout<<1<<"\n";

    }
    else{
        fout<<st<<"\n";
        }





    return 0;
}