#include<stdio.h>
#include<algorithm>
#include<string.h>
#include<string>
#include<vector>
#include<iostream>
#include<map>
using namespace std;
#define MP make_pair
#define REP(i, N) for(int i = 0; i<(N); i++)
const int INF = 987654321;
int N;
struct dap{
int score;
int time;
int ind;
};
bool operator<(const dap& lhs, const dap& rhs){
if(lhs.score > rhs.score)return true;
else if(lhs.score < rhs.score)return false;
if(lhs.time < rhs.time)return true;
else return false;
}
int main(){
int numC;
//scanf("%d ", &numC);
//while(numC--){
scanf("%d ", &N);
vector<dap> score(N);
REP(i, N){
scanf("%d %d ", &score[i].time, &score[i].score);
score[i].ind = i+1;
}
sort(score.begin(), score.end());
if(score[0].score == 0)printf("0\n");
else{
printf("%d\n", score[0].time + (score[0].ind - 1)*20);
}
//}
return 0;
}
