#include <iostream>
#include <math.h>

using namespace std;

int main()
{
    int n,s;
    cin>>n;
    if(n%10==7)
        s=int((n-1)*log((double)2)/log((double)10));
    else
        s=int(n * log((double)2)/log((double)10));
    cout<<s<<endl;
    return 0;
}

What is lacking in terms? What could I forget?