#include <iostream>
#include<tgmath.h>
using namespace std;
int main() {
// your code goes here
int t;
cin>>t;
int k = log(25)/log(5);
cout<<k;
return 0;
}
I2luY2x1ZGUgPGlvc3RyZWFtPgojaW5jbHVkZTx0Z21hdGguaD4KdXNpbmcgbmFtZXNwYWNlIHN0ZDsKCgppbnQgbWFpbigpIHsKCS8vIHlvdXIgY29kZSBnb2VzIGhlcmUKCiAgICBpbnQgdDsKICAgIGNpbj4+dDsKICAgIGludCBrID0gbG9nKDI1KS9sb2coNSk7CiAgICBjb3V0PDxrOwoJcmV0dXJuIDA7Cn0K