without round function i got WA #14. When i used it i got AC!
#include <iostream>
#include <cmath>
using namespace std;
double round(double d);
int main()
{double P, Q;
#ifndef ONLINE_JUDGE
 freopen("input.txt", "r", stdin);
 freopen("output.txt", "w", stdout);
#endif
 cin>>P>>Q;
 P/=100;
 Q/=100;
 int i=2;
 while(true)
    {double min=round(i*P);
     double max=round(i*Q);
     int C=int(max);
     if(C>min && C<max && C>=1) break;
     i++;
    }
 cout<<i;
    return 0;
}
//---------------------------------------------------------------------------
double round(double d)
{return floor(d*10000+0.5)/10000;
}

thanks