#include <stdio.h>
int max(int a,int b){
if(a>b)return a;
return b;
}
int main(){
int n,a,b,temp;
while(1){
scanf("%d",&n);
if(n==0)return 0;
a=b=0;
for(int i=2;i<n;i++){
temp=i;
while(temp%2==0){
temp/=2;
a++;
}
while(temp%5==0){
temp/=5;
b++;
}

}
printf("%d\n",max(a,b));
}
}