#include <stdio.h>
 
int main() {
	int n,m;
	scanf("%d %d",&n,&m);
 
	int package[m], each[m], min = 1000;
	for(int i = 0 ; i < m ; i++){
		scanf("%d %d",&package[i],&each[i]);
		int OnlyPackage = ((n/6)+1)*package[i];
		int OnlyEach = n*each[i];
		int Set = (n/6*package[i]) + (n%6*each[i]);
 
		min = (OnlyPackage < min ? OnlyPackage : min);
		min = (OnlyEach < min ? OnlyEach : min);
		min = (Set < min ? Set : min);
	}
 
    printf("%d",min);
 
    return 0;
}
 

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NyAyCjEwIDMKMTIgMg==

7 2
10 3
12 2