#include <iostream>
#include <cmath>
using namespace std;
int main() {
int n, k, minP = 1000, minS = 1000;
cin >> n >> k;
int packets[k * 2] = {0};
for(int i = 0 ; i < (k * 2) ; i++){
cin >> packets[i];
if(i % 2 == 0)
minP = min(minP, packets[i]);
else
minS = min(minS, packets[i]);
}
int Pp = minP * ( (n / 6) + ((n % 6 == 0)?0 : 1) );
int Sp = minS * n;
if(Sp <= Pp){
cout << Sp << endl;
return 0;
}
return 0;
}
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