#include <iostream>
using namespace std;
int main ()
{
cout<<(1*15*20-1*20*10)/(20-10);
return 0;
}

#include<bits/stdc++.h>
using namespace std;

long long a,b,c,d,e,f,g;
const int N=1e6+10;
double x,y,z;
int n[N];

int main(){
	cout<<10;
	return 0;
}

#include<iostream>
using namespace std;
int main()
{
	cout <<10;	
	return 0;
}

#include<iostream>using namespace std;int main(){cout<<"10";return 0;} 最简

#include<iostream>
using namespace std;
int main()
{
	cout << (15*20-20*10)/(20-10);	
	return 0;
}