#include<fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

int f(long long n){

int nr=0;

while(n && n%5==0){
    nr++;
    n/=5;
}

return nr;

}

int main(){

int p;

long long i,cnt=0;

fin>>p;

if(p==0){
    fout<<0;
    return 0;
}

for(i=5;cnt<p;i+=5){
    cnt=cnt + f(i); /// la ce putere apare 5 in descp. lui i
}

fout<<i-5;

}