#include <stdio.h>
#include <math.h>
long long p;
long long n;
void citire(){
     FILE *in;
     in=fopen("fact.in","r");

     fscanf(in,"%lld",&p);   
     fclose(in); 
     }
     
void scriere(){
FILE *out;
     out=fopen("fact.out","w");
     fprintf(out,"%lld",n);
     fclose(out);
     }

double nrz(long long i){
double x,k,sum;
sum=0;
x=ceil(log(i)/log(5));
 for(k=1;k<=x;k++){
                  sum=sum+floor(i/pow(5,k));
                  }
 return sum;
}

void procesare(){
long long i;
long long a=0;
n=1;
if(p>0){
 for(i=5;i<=50000000;i+=1){
  a=a+nrz(i);
  if(a==p){ n=i;break; }
  if(a>p) { n=-1;break;}
}
 }
 }
     
int main(){
 citire();
 procesare();
 scriere();
 return 0;   
}