#include<bits/stdc++.h>
#define Gc() getchar() 
#define Me(x,y) memset(x,y,sizeof(x))
#define Mc(x,y) memcpy(x,y,sizeof(x))
#define d(x,y) ((m)*(x-1)+(y))
#define R(n) (rnd()%(n)+1)
#define Pc(x) putchar(x)
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
using namespace std;using ll=long long;using db=double;using lb=long db;using ui=unsigned;using ull=unsigned long long;using pii=pair<int,int>;using LL=__int128;
const int N=1e5+5,M=1e5,K=600+5,mod=1e9+7,Mod=mod-1;const db eps=1e-6;const ll INF=1e18+7;mt19937 rnd(263082);
int n,m,Mx,A[N],B[N],C[N];ll f[N],st[N][20];
ll qry(int x,int y){
	int d=__lg(y-x+1);return min(st[x+(1<<d)-1][d],st[y][d]);
}
void trans(int x){
	int i,j;int y=A[x]-1;
	for(i=1;i<=min(y,x-1);i=j+1){
		j=min(y/(y/i),x-1);
		f[x]=min(f[x],qry(i,j)+1ll*y/i*x-(A[x]-1)/Mx*x);
	}
}
void Solve(){
	int i,j;scanf("%d%d",&n,&m);
	ll sum=0;Mx=m;Me(A,0x3f);
	for(i=1;i<=n;i++) scanf("%d%d",&B[i],&C[i]),Mx=max(Mx,B[i]);
	for(i=1;i<=n;i++) {sum+=(C[i]-1)/Mx*B[i];A[B[i]]=min(A[B[i]],C[i]);}
	Me(f,0x3f);f[m]=0;
	for(i=1;i<=Mx;i++){
		if(A[i]<=M) trans(i);
		for(st[i][0]=f[i],j=1;(1<<j)<=i;j++) st[i][j]=min(st[i][j-1],st[i-(1<<j-1)][j-1]);
		// cerr<<f[i]<<' ';
	}
	printf("%lld\n",f[Mx]+sum);
}
int main(){
	int t=1;
	// scanf("%d",&t);
	while(t--) Solve();
	cerr<<clock()*1.0/CLOCKS_PER_SEC<<'\n';
}