#include <fstream>
#define MAX 500000000
using namespace std;
long p;

int f(int k){
    long m=5,z=0;
    while(k/m!=0){
    z+=k/m;
    m*=5;
    }
   return z;
}

int bin_search(long l,long r){
    if(l>r) return -1;
    else{
          long c=(l+r)/2;
          if(f(c)<p) bin_search(c+1,r);
          else
               if(f(c)>p) bin_search(l,c-1);
               else
                    return c;
    }
}


int main(){
ifstream f("fact.in");
ofstream g("fact.out");

f>>p;

long n=bin_search(0,MAX);

g<<n;


}