#include<stdio.h>

int fac(int n) {
if ( n == 0 )
	return 1;
else return n*fac(n-1);
}


int main(){
int stanga=0;
int dreapta = 888888;
int n=0,p;
FILE *in,*out;
int temp=0,temp1=0;
in = fopen("fact.in","r");
fscanf(in,"%d",&p);

  if (p !=0 ){
	while (n) {
		int mij=(stanga+dreapta)/2;
		while(temp<p){
			n++;
			mij=n;
			while(mij%5==0){
				temp++;
				mij=mij/5;
			}
		}
		if ( nrz==p && stanga==dreapta){
			n=stanga;
			break;
		}
		if (dreapta<stanga)
		{
			n=-1;
			break;
		}
		if (p>nrz) stanga = mij+1;
		else dreapta=mij-1;
	}
  }


fclose(in);
out = fopen("fact.out","w");
fprintf(out,"%d",n);
fclose(out);
return 0;
}